Warning signs of the disorder include:

- A child who has one or more medical problems that do not respond to treatment or that follow an unusual course that is persistent, puzzling, and unexplained.

- Physical or laboratory findings that are highly unusual, discrepant with patient's presentation or history, or physically or clinically impossible.

- A parent who appears medically knowledgeable, fascinated with medical details and hospital gossip, appears to enjoy the hospital environment and expresses interest in the details of other patients' problems.

- A highly attentive parent who is reluctant to leave their child's side and who themselves seem to require constant attention.

- A parent who appears unusually calm in the face of serious difficulties in their child's medical course while being highly supportive and encouraging of the physician, or one who is angry, devalues staff and demands further intervention, more procedures, second opinions, and transfers to other more sophisticated facilities.

- The suspected parent may work in the health care field themselves or profess an interest in a health-related job.

- The signs and symptoms of a child's illness may lessen or simply vanish in the parent's absence (hospitalization and careful monitoring may be necessary to establish this causal relationship).

- A family history of similar or unexplained illness or death in a sibling.

- A parent with symptoms similar to their child's own medical problems or an illness history that itself is puzzling and unusual.

- A suspected emotionally distant relationship between parents; the spouse often fails to visit the patient and has little contact with physicians even when the child is hospitalized with a serious illness.

- A parent who reports dramatic, negative events, such as house fires, burglaries, or car accidents, that affect them and their family while their child is undergoing treatment.

- A parent who seems to have an insatiable need for adulation or who makes self-serving efforts for public acknowledgment of their abilities.

- A patient who inexplicably deteriorates whenever discharge is planned.

In factitious disorder imposed on another, a caregiver makes a dependent person appear mentally or physically ill in order to gain attention. To perpetuate the medical relationship, the caregiver systematically misrepresents symptoms, fabricates signs, manipulates laboratory tests, or even purposely harms the dependent (e.g. by poisoning, suffocation, infection, physical injury). Studies have shown a mortality rate of between 6% and 10%, making it perhaps the most lethal form of abuse.

At the time of diagnosis, the average age of the persons affected was 4 years. Slightly over 50% were aged 24 months or younger, and 75% were under 6 years old. The average duration from onset of symptoms to diagnosis was 22 months. By the time of diagnosis, 6% of the affected persons were dead, mostly from apnea (a common result of smothering) or starvation, and 7% suffered long-term or permanent injury. About half of the affected had siblings; 25% of the known siblings were dead, and 61% of siblings had symptoms similar to the affected or that was otherwise suspicious. The mother was the perpetrator in 76.5% of the cases, the father in 6.7%.

Most present about 3 medical problems in some combination of the 103 different reported symptoms. The most frequently reported problems are apnea (26.8% of cases), anorexia / feeding problems (24.6% of cases), diarrhea (20%), seizures (17.5%), cyanosis (blue skin) (11.7%), behavior (10.4%), asthma (9.5%), allergy (9.3%), and fevers (8.6%). Other symptoms include failure to thrive, vomiting, bleeding, rash and infections. Many of these symptoms are easy to fake because they are subjective. A parent reporting that their child had a fever in the past 24 hours is making a claim that is impossible to prove or disprove. The number and variety of presented symptoms contribute to the difficulty in reaching a proper MSbP diagnosis.

Aside from the motive (which is to gain attention or sympathy), another feature that differentiates MSbP from "typical" physical child abuse is the degree of premeditation involved. Whereas most physical abuse entails lashing out at a child in response to some behavior (e.g., crying, bedwetting, spilling food), assaults on the MSbP victim tend to be unprovoked and planned.

Also unique to this form of abuse is the role that health care providers play by actively, albeit unintentionally, enabling the abuse. By reacting to the concerns and demands of perpetrators, medical professionals are manipulated into a partnership of child maltreatment. Challenging cases that defy simple medical explanations may prompt health care providers to pursue unusual or rare diagnoses, thus allocating, even more, time to the child and the abuser. Even without prompting, medical professionals may be easily seduced into prescribing diagnostic tests and therapies that are at best uncomfortable and costly, and at worst potentially injurious to the child. If the health practitioner instead resists ordering further tests, drugs, procedures, surgeries, or specialists, the MSbP abuser makes the medical system appear negligent for refusing to help a poor sick child and their selfless parent. Like those with Munchausen syndrome, MSbP perpetrators are known to switch medical providers frequently until they find one that is willing to meet their level of need; this practice is known as "doctor shopping" or "hospital hopping".

The perpetrator continues the abuse because maintaining the child in the role of patient satisfies the abuser's needs. The cure for the victim is to separate the child completely from the abuser. When parental visits are allowed, sometimes there is a disastrous outcome for the child. Even when the child is removed, the perpetrator may then abuse another child: a sibling or other child in the family.

Factitious disorder imposed on another can have many long-term emotional effects on a child. Depending on their experience of medical interventions, a percentage of children may learn that they are most likely to receive the positive maternal attention they crave when they are playing the sick role in front of health care providers. Several case reports describe Munchausen syndrome patients suspected of themselves having been MSbP victims. Seeking personal gratification through illness can thus become a lifelong and multi-generational disorder in some cases. In stark contrast, other reports suggest survivors of MSbP develop an avoidance of medical treatment with post-traumatic responses to it. This variation possibly reflects broad statistics on survivors of child abuse in general, where around 30% go on to also become abusers even though a significant percentage do not.

The adult care provider who has abused the child often seems comfortable and not upset over the child's hospitalization. While the child is hospitalized, medical professionals must monitor the caregiver's visits to prevent an attempt to worsen the child's condition. In addition, in many jurisdictions, medical professionals have a duty to report such abuse to legal authorities.

Diagnosing factitious disorder imposed on self requires a clinical assessment. Clinicians should be aware that those presenting with symptoms (or persons reporting for that person) may malinger, and caution should be taken to ensure there is evidence for a diagnosis. Lab tests may be required, including complete blood count (CBC), urine toxicology, drug levels from blood, cultures, coagulation tests, assays for thyroid function, or DNA typing. In some cases CT scan, magnetic resonance imaging, psychological testing, electroencephalography, or electrocardiography may also be employed. A summary of more common and reported cases of factitious disorder (Munchausen syndrome), and the laboratory tests used to differentiate these from authentic disease is provided below:

There are several symptoms that together point to factitious disorder, including frequent hospitalizations, knowledge of several illnesses, frequently requesting medication such as pain killers, openness to extensive surgery, few or no visitors during hospitalizations, and exaggerated or fabricated stories about several medical problems. Factitious disorder should not be confused with hypochondria, as people with factitious disorder syndrome do not really believe they are sick; they only want to be sick, and thus fabricate the symptoms of an illness. It is also not the same as pretending to be sick for personal benefit such as being excused from work or school.

People may fake their symptoms in multiple ways. Other than making up past medical histories and faking illnesses, people might inflict harm on themselves by consuming laxatives or other substances, self-inflicting injury to induce bleeding, and altering laboratory samples.” Many of these conditions do not have clearly observable or diagnostic symptoms and sometimes the syndrome will go undetected because patients will fabricate identities when visiting the hospital several times. Factitious disorder has several complications, as these people will go to great lengths to fake their illness. Severe health problems, serious injuries, loss of limbs or organs, and even death are possible complications.

In factitious disorder imposed on self, the affected person exaggerates or creates symptoms of illnesses in themselves to gain examination, treatment, attention, sympathy, and/or comfort from medical personnel. In some extreme cases, people suffering from Munchausen syndrome are highly knowledgeable about the practice of medicine and are able to produce symptoms that result in lengthy and costly medical analysis, prolonged hospital stays, and unnecessary operations. The role of "patient" is a familiar and comforting one, and it fills a psychological need in people with this syndrome. This disorder is distinct from hypochondriasis and other somatoform disorders in that those with the latter do not intentionally produce their somatic symptoms. Munchausen syndrome is distinct from other psychiatric disorders such as malingering in that Munchausen does not fabricate symptoms for material gain such as financial compensation, absence from work, or access to drugs.

Risk factors for developing factitious disorder include childhood traumas, growing up with parents/caretakers who were emotionally unavailable due to illness or emotional problems, a serious illness as a child, failed aspirations to work in the medical field, personality disorders, and low self-esteem. Factitious disorder is more common in men and is seen in young or middle-aged adults. Those with a history of working in healthcare are also at greater risk of developing it.

Arrhythmogenic Munchausen syndrome describes individuals who simulate or stimulate cardiac arrhythmias to gain medical attention.

A similar behavior called factitious disorder imposed on another has been documented in the parent or guardian of a child. The adult ensures that his or her child will experience some medical affliction, therefore compelling the child to suffer through treatments and spend a significant portion of their youth in hospitals. Furthermore, a disease may actually be initiated in the child by the parent or guardian. This condition is considered distinct from Munchausen syndrome. There is growing consensus in the pediatric community that this disorder should be renamed "medical abuse" to highlight the harm caused by the deception and to make it less likely that a perpetrator can use a psychiatric defense when harm is done.

Previously, the DSM-IV differentiated among three types:

- Factitious disorders with predominantly psychological signs and symptoms: if psychological signs and symptoms predominate in the clinical presentation

- Factitious disorders with predominantly physical signs and symptoms: if physical signs and symptoms predominate in the clinical presentation

- Factitious disorders with combined psychological and physical signs and symptoms: if both psychological and physical signs and symptoms are present and neither predominates in the clinical presentation

Ganser syndrome was once considered a separate factitious disorder. It is a disorder of extreme stress or an organic condition. The patient suffers from approximation or giving absurd answers to simple questions. The syndrome is sometimes diagnosed as merely malingering—however, it is more often defined as a factitious disorder. This has been seen in prisoners following solitary confinement, and the symptoms are consistent in different prisons, though the patients do not know one another.

Symptoms include a clouding of consciousness, somatic conversion symptoms, confusion, stress, loss of personal identity, echolalia, and echopraxia. Individuals also give approximate answers to simple questions such as, "How many legs on a cat?" "Three"; "What's the day after Wednesday?" "Friday"; and so on. The disorder is extraordinarily rare with fewer than 100 recorded cases. While individuals of all backgrounds have been reported with the disorder, there is a higher inclination towards males (75% or more). The average age of those with Ganser syndrome is 32, though it stretches from ages 15–62 years old.

People who demonstrate factitious disorders often claim to have physical ailments or be recovering from the consequences of stalking, victimization, harassment, and sexual abuse. Several behaviors present themselves to suggest factors beyond genuine problems. After studying 21 cases of deception, Feldman listed the following common behavior patterns in people who exhibited Munchausen by Internet:

- Medical literature from websites or textbooks is often duplicated or discussed in great detail.

- The length and severity of purported physical ailments conflicts with user behavior. Feldman uses the example of someone posting in considerable detail about being in septic shock, when such a possibility is extremely unlikely.

- Symptoms of ailments may be exaggerated as they correspond to a user's misunderstanding of the nature of an illness.

- Grave situations and increasingly critical prognoses are interspersed with "miraculous" recoveries.

- A user's posts eventually reveal contradictory information or claims that are implausible: for example, other users of a forum may find that a user has been divulging contradictory information about occurrence or length of hospital visits.

- When attention and sympathy decreases to focus on other members of the group, a user may announce that other dire events have transpired, including the illness or death of a close family member.

- When faced with insufficient expressions of attention or sympathy, a forum member claims this as a cause that symptoms worsen or do not improve.

- A user resists contact beyond the Internet, such as by telephone or personal visit, often claiming bizarre reasons for not being able to accept such contact.

- Further emergencies are described with inappropriate happiness, designed to garner immediate reactions.

- The posts of other forum members exhibit identical writing styles, spelling errors, and language idiosyncrasies, suggesting that the user has created fictitious identities to move the conversation in their direction.

Munchausen by Internet is a pattern of behavior akin to Munchausen syndrome (renamed factitious disorder imposed on self), a psychiatric disorder, wherein those affected feign disease, illness, or psychological trauma to draw attention, sympathy, or reassurance to themselves. In Munchausen by internet, users seek attention by feigning illnesses in online venues such as chat rooms, message boards, and Internet Relay Chat (IRC). It has been described in medical literature as a manifestation of factitious disorder imposed on self, or if claiming illness of a child or other family member, factitious disorder imposed on another. Reports of users who deceive Internet forum participants by portraying themselves as gravely ill or as victims of violence first appeared in the 1990s due to the relative newness of Internet communications. The pattern was identified in 1998 by psychiatrist Marc Feldman, who created the term "Münchausen by Internet" in 2000. It is not included in the fifth revision of the "Diagnostic and Statistical Manual of Mental Disorders" (DSM-5).

The development of factitious disorders in online venues is made easier by the availability of medical literature on the Internet, the anonymous and malleable nature of online identities, and the existence of communication forums established for the sole purpose of giving support to members facing significant health or psychological problems. Several high-profile cases have demonstrated behavior patterns which are common among those who pose as gravely ill or as victims of violence, or whose deaths are announced to online forums. The virtual communities that were created to give support, as well as general non-medical communities, often express genuine sympathy and grief for the purported victims. When fabrications are suspected or confirmed, the ensuing discussion can create schisms in online communities, destroying some and altering the trusting nature of individual members in others.

The likely course and outcome of mental disorders varies and is dependent on numerous factors related to the disorder itself, the individual as a whole, and the social environment. Some disorders are transient, while others may be more chronic in nature.

Even those disorders often considered the most serious and intractable have varied courses i.e. schizophrenia, psychotic disorders, and personality disorders. Long-term international studies of schizophrenia have found that over a half of individuals recover in terms of symptoms, and around a fifth to a third in terms of symptoms and functioning, with some requiring no medication. At the same time, many have serious difficulties and support needs for many years, although "late" recovery is still possible. The World Health Organization concluded that the long-term studies' findings converged with others in "relieving patients, carers and clinicians of the chronicity paradigm which dominated thinking throughout much of the 20th century."

Around half of people initially diagnosed with bipolar disorder achieve syndromal recovery (no longer meeting criteria for the diagnosis) within six weeks, and nearly all achieve it within two years, with nearly half regaining their prior occupational and residential status in that period. However, nearly half go on to experience a new episode of mania or major depression within the next two years. Functioning has been found to vary, being poor during periods of major depression or mania but otherwise fair to good, and possibly superior during periods of hypomania in Bipolar II.

The definition and classification of mental disorders are key issues for researchers as well as service providers and those who may be diagnosed. For a mental state to classify as a disorder, it generally needs to cause dysfunction. Most international clinical documents use the term mental "disorder", while "illness" is also common. It has been noted that using the term "mental" (i.e., of the mind) is not necessarily meant to imply separateness from brain or body.

According to DSM-IV, a mental disorder is a psychological syndrome or pattern which is associated with distress (e.g. via a painful symptom), disability (impairment in one or more important areas of functioning), increased risk of death, or causes a significant loss of autonomy; however it excludes normal responses such as grief from loss of a loved one, and also excludes deviant behavior for political, religious, or societal reasons not arising from a dysfunction in the individual.

DSM-IV precedes the definition with caveats, stating that, as in the case with many medical terms, "mental disorder" "lacks a consistent operational definition that covers all situations", noting that different levels of abstraction can be used for medical definitions, including pathology, symptomology, deviance from a normal range, or etiology, and that the same is true for mental disorders, so that sometimes one type of definition is appropriate, and sometimes another, depending on the situation.

In 2013, the American Psychiatric Association (APA) redefined mental disorders in the DSM-5 as "a syndrome characterized by clinically significant disturbance in an individual's cognition, emotion regulation, or behavior that reflects a dysfunction in the psychological, biological, or developmental processes underlying mental functioning.”

The Truman Show delusion, informally known as Truman syndrome, is a type of delusion in which the person believes that their lives are staged reality shows, or that they are being watched on cameras. The term was coined in 2008 by brothers Joel Gold and Ian Gold, a psychiatrist and a neurophilosopher, respectively, after the film "The Truman Show".

The Truman Show delusion is not officially recognized nor listed in the "Diagnostic and Statistical Manual of the American Psychiatric Association".

Cyberchondria, otherwise known as 'compucondria', is the unfounded escalation of concerns about common symptomology based on review of search results and literature online. Articles in popular media position cyberchondria anywhere from temporary neurotic excess to adjunct hypochondria. Cyberchondria is a growing concern among many healthcare practitioners as patients can now research any and all symptoms of a rare disease, illness or condition, and manifest a state of medical anxiety.

In "How Everyone Became Depressed: The Rise and Fall of the Nervous Breakdown" (2013), Edward Shorter, a professor of psychiatry and the history of medicine, argues for a return to the old-fashioned concept of nervous illness:

Latah, from Southeast Asia, is a condition in which abnormal behaviors result from a person experiencing a sudden shock. When surprised, the affected person typically engages in such behaviors as screaming, cursing, dancing type movements, and uncontrollable laughter, and will typically mimic the words or actions of those around them. Physical symptoms include an increased heart rate and profuse sweating, but no clear physiological source has been identified.

Latah is considered a culture-specific startle disorder that was historically regarded as personal difference rather than an illness.

Similar conditions have been recorded within other cultures and locations. For example, there are the so-called Jumping Frenchmen of Maine, the women of the Ainu people of Japan ("imu"), the Siberian ("miryachit"), and the Filipino and Thai peoples; however, the connection among these syndromes is controversial.

The terms "nervous breakdown" and "mental breakdown" have not been formally defined through a medical diagnostic system such as the DSM-5 or ICD-10, and are nearly absent from current scientific literature regarding mental illness. Although "nervous breakdown" is not rigorously defined, surveys of laypersons suggest that the term refers to a specific acute time-limited reactive disorder, involving symptoms such as anxiety or depression, usually precipitated by external stressors. Many health experts today refer to a nervous breakdown as a "modern mental health crisis."

Specific cases are sometimes described as a "breakdown" only after the emotional and physical demands on a person's life are so great as to prevent him or her from performing activities of daily living or, less strictly, only when those demands prevent him/her from performing his/her familial or occupational duties.

Nervous breakdowns are often caused by serious ongoing mental health disorders.

Qualities of MPI outbreaks often include:

- symptoms that have no plausible organic basis;

- symptoms that are transient and benign;

- symptoms with rapid onset and recovery;

- occurrence in a segregated group;

- the presence of extraordinary anxiety;

- symptoms that are spread via sight, sound or oral communication;

- a spread that moves down the age scale, beginning with older or higher-status people;

- a preponderance of female participants

Also, the illness may recur after the initial outbreak.

Latah can affect people differently; someone can have a very strong reaction or a slight reaction during a latah episode. Every instance of latah has been acquired over time. Those who are affected, which by an overwhelming number are middle-to-older-aged women, are not born latah. It typically occurs around the time of menopause. There is a lack of latah in the higher social strata of Malay and Java, which suggests they are more likely to suppress their responses than those who belong to lower social classes.

A latah episode occurs after a startle of some sort (poking, shouting, something falling). During an episode, a latah person will begin to shout obscenities, imitate words or gestures of those around them or even those on TV, and will often obey any commands given to them – no matter how outrageous or against cultural norms they are. Persons with latah make movements reminiscent of behaviors normally peculiar to certain childhood developmental stages. The person is unlikely to remember anything occurring during the episode.

Diagnosis of a specific type of delusional disorder can sometimes be made based on the content of the delusions. The "Diagnostic and Statistical Manual of Mental Disorders" (DSM) enumerates seven types:

- Erotomanic type (erotomania): delusion that another person, often a prominent figure, is in love with the individual. The individual may breach the law as he/she tries to obsessively make contact with the desired person.

- Grandiose type: delusion of inflated worth, power, knowledge, identity or believes themself to be a famous person, claiming the actual person is an impostor or an impersonator.

- Jealous type: delusion that the individual's sexual partner is unfaithful when it is untrue. The patient may follow the partner, check text messages, emails, phone calls etc. in an attempt to find "evidence" of the infidelity.

- Persecutory type: This delusion is a common subtype. It includes the belief that the person (or someone to whom the person is close) is being malevolently treated in some way. The patient may believe that he/she has been drugged, spied upon, harassed and so on and may seek "justice" by making police reports, taking court action or even acting violently.

- Somatic type: delusions that the person has some physical defect or general medical condition

- Mixed type: delusions with characteristics of more than one of the above types but with no one theme predominating.

- Unspecified type: delusions that cannot be clearly determined or characterized in any of the categories in the specific types.

The following can indicate a delusion:

1. The patient expresses an idea or belief with unusual persistence or force.

2. That idea appears to have an undue influence on the patient's life, and the way of life is often altered to an inexplicable extent.

3. Despite his/her profound conviction, there is often a quality of secretiveness or suspicion when the patient is questioned about it.

4. The individual tends to be humorless and oversensitive, especially about the belief.

5. There is a quality of "centrality": no matter how unlikely it is that these strange things are happening to him/her, the patient accepts them relatively unquestioningly.

6. An attempt to contradict the belief is likely to arouse an inappropriately strong emotional reaction, often with irritability and hostility.

7. The belief is, at the least, unlikely, and out of keeping with the patient's social, cultural, and religious background.

8. The patient is emotionally over-invested in the idea and it overwhelms other elements of their psyche.

9. The delusion, if acted out, often leads to behaviors which are abnormal and/or out of character, although perhaps understandable in the light of the delusional beliefs.

10. Individuals who know the patient observe that the belief and behavior are uncharacteristic and alien.

Additional features of delusional disorder include the following:

1. It is a primary disorder.

2. It is a stable disorder characterized by the presence of delusions to which the patient clings with extraordinary tenacity.

3. The illness is chronic and frequently lifelong.

4. The delusions are logically constructed and internally consistent.

5. The delusions do not interfere with general logical reasoning (although within the delusional system the logic is perverted) and there is usually no general disturbance of behavior. If disturbed behavior does occur, it is directly related to the delusional beliefs.

6. The individual experiences a heightened sense of self-reference. Events which, to others, are nonsignificant are of enormous significance to him or her, and the atmosphere surrounding the delusions is highly charged.

Dual diagnosis (also called co-occurring disorders, COD, or dual pathology) is the condition of suffering from a mental illness and a comorbid substance abuse problem. There is considerable debate surrounding the appropriateness of using a single category for a heterogeneous group of individuals with complex needs and a varied range of problems. The concept can be used broadly, for example depression and alcoholism, or it can be restricted to specify severe mental illness (e.g. psychosis, schizophrenia) and substance misuse disorder (e.g. cannabis abuse), or a person who has a milder mental illness and a drug dependency, such as panic disorder or generalized anxiety disorder and is dependent on opioids. Diagnosing a primary psychiatric illness in substance abusers is challenging as drug abuse itself often induces psychiatric symptoms, thus making it necessary to differentiate between substance induced and pre-existing mental illness.

Those with co-occurring disorders face complex challenges. They have increased rates of relapse, hospitalization, homelessness, and HIV and hepatitis C infection compared to those with either mental or substance use disorders alone. The cause of co-occurring disorders is unknown, although there are several theories.

Mass psychogenic illness (MPI), also called mass sociogenic illness or just sociogenic illness, is "the rapid spread of illness signs and symptoms affecting members of a cohesive group, originating from a nervous system disturbance involving excitation, loss, or alteration of function, whereby physical complaints that are exhibited unconsciously have no corresponding organic" cause. MPI is distinct from other collective delusions, also included under the blanket terms of mass hysteria, in that MPI causes symptoms of disease, though there is no organic cause.

There is a clear preponderance of female victims. The DSM-IV-TR does not have specific diagnosis for this condition but the text describing conversion disorder states that "In 'epidemic hysteria', shared symptoms develop in a circumscribed group of people following 'exposure' to a common precipitant."

Depressive Disorder Not Otherwise Specified (DD-NOS) is designated by the code "311" in the DSM-IV for depressive disorders that are impairing but do not fit any of the officially specified diagnoses. According to the DSM-IV, DD-NOS encompasses "any depressive disorder that does not meet the criteria for a specific disorder." In the DSM-5, it is called unspecified depressive disorder.

Examples of disorders in this category include those sometimes described as minor depressive disorder and recurrent brief depression.

"Depression" refers to a spectrum of disturbances in mood that vary from mild to severe and from short periods to constant illness. DD-NOS is diagnosed if a patients symptoms fail to meet the criteria more common depressive disorders such as major depressive disorder or dysthymia. Although DD-NOS shares similar symptoms to dysthymia, dysthymia is classified by a period of at least 2 years of constantly recurring depressed mood, where as DD-NOS is classified by much shorter periods of depressed moods.

For most people who suffer the condition, their life will be significantly affected. DD-NOS can make many aspects of a person's daily life difficult to manage, inhibiting their ability to enjoy the things that used to make them happy. Sufferers of the disorder tend to isolate themselves from their friends and families, lose interest in some activities, and experience behavioural changes and sleeping disorders. Some sufferers also experience suicidal tendencies or suicide attempts. In addition to having these symptoms, a diagnosis of DD-NOS will only be made if the symptoms cause significant distress or impairment in social, occupational, or other important areas of functioning. For the diagnosis to be accurate, a psychiatrist is required to spend extensive time with the patient.

Symptoms of the disorder may arise due to several reasons. These include:

- Distress due to medical conditions

- Environmental effects and situations

However, the effects of drugs or medication or bereavement are not classified under the diagnosis.

A person will not be diagnosed with the condition if they have or have had any of the following: a major depressive episode, manic episode, mixed episode or hypomanic episode.

A diagnosis of the disorder will look like: "Depressive Disorder NOS 311".

Delusions – fixed, fallacious beliefs – are symptoms that, in the absence of organic disease, indicate psychiatric disease. The content of delusions varies considerably (limited by the imagination of the delusional person), but certain themes have been identified; for example persecution. These themes have diagnostic importance in that they point to certain diagnoses. Persecutory delusions are, for instance, classically linked to psychosis.

311- Depressive Disorder Not Otherwise Specified (NOS)

The Depressive disorder NOS category includes disorders with depressive features that do not meet the criteria for Major Depressive Disorder, Dysthymic disorder, Adjustment Disorder with Depressed Mood or Adjustment Disorder with Mixed Anxiety and Depressed Mood. Sometimes depressive symptoms can present as part of an Anxiety Disorder Not otherwise Specified. Examples of Depressive Disorder Not Otherwise Specified include.

- Premenstrual Dysphoric Disorder: in most menstrual cycles during the past years, (e.g., markedly depressed mood, marked anxiety, marked affective lability, or decreased interest in activities) regularly occurred during the onset of menses. These symptoms must be severe enough to markedly interfere with work, school, or usual activities and be entirely absent for at least 1 week post menses.

- Minor depressive disorder: episodes of at least 2 weeks of depressive symptoms but with fewer than the five items required for Major Depressive Disorder.

- Recurrent brief depressive disorder: depressive episodes lasting from 2 days up to 2 weeks, occurring at least once a month for 12 months (not associated with the menstrual cycle)

- Post psychotic depressive Disorder of schizophrenia: a Major Depressive Episode that occurs during the residual phase of schizophrenia.

- A Major Depressive Episode superimposed on delusional disorder, Psychotic Disorder Not Otherwise Specified, or the active phase of schizophrenia.

- Situations in which the clinician has concluded that a depressive disorder is present but is unable to determine whether it is primary, due to a general medical condition, or substance induced.

Symptoms of the disorder may arise due to several reasons. These include:

- Distress due to medical conditions

- Environmental effects and situations

Rumination syndrome is a condition which affects the functioning of the stomach and esophagus, also known as a "functional gastroduodenal disorder." In patients that have a history of eating disorders, Rumination syndrome is grouped alongside eating disorders such as bulimia and pica, which are themselves grouped under non-psychotic mental disorder. In most healthy adolescents and adults who have no mental disability, Rumination syndrome is considered a motility disorder instead of an eating disorder, because the patients tend to have had no control over its occurrence and have had no history of eating disorders.