Somatic manifestations of MD are distinguished by an extreme diversity and include headaches, back pain, abdominal pain etc. Pathological behaviour masking depression may take the form of compulsive gambling, compulsive work, changes in arousal or orgasmic function, decreased libido or, on the contrary, impulsive sexual behaviour, alcoholism, drug addiction and more.

Masked depression (MD) was a proposed form of atypical depression in which somatic symptoms or behavioural disturbances dominate the clinical picture and disguise the underlying affective disorder. The concept is not currently supported by the mental health profession.

Conversion disorder is now contained under the umbrella term functional neurological symptom disorder. In cases of conversion disorder, there is a psychological stressor.

The diagnostic criteria for functional neurological symptom disorder, as set out in DSM-V, are:

Specify type of symptom or deficit as:

- With weakness or paralysis

- With abnormal movement (e.g. tremor, dystonic movement, myoclonus, gait disorder)

- With swallowing symptoms

- With speech symptoms (e.g. dysphonia, slurred speech)

- With attacks or seizures

- With amnesia or memory loss

- With special sensory symptom (e.g. visual, olfactory, or hearing disturbance)

- With mixed symptoms.

Specify if:

- Acute episode: symptoms present for less than six months

- Persistent: symptoms present for six months or more.

Specify if:

- Psychological stressor (conversion disorder)

- No psychological stressor (functional neurological symptom disorder)

Pan-Neurosis is the existence of multiple neurotic symptoms such as:

- obsessions

- compulsions

- phobias

- hysteria

- depression

- hypochondriasis

- depersonalization

Conversion disorder begins with some stressor, trauma, or psychological distress. Usually the physical symptoms of the syndrome affect the senses or movement. Common symptoms include blindness, partial or total paralysis, inability to speak, deafness, numbness, difficulty swallowing, incontinence, balance problems, seizures, tremors, and difficulty walking. These symptoms are attributed to conversion disorder when a medical explanation for the afflictions cannot be found. Symptoms of conversion disorder usually occur suddenly. Conversion disorder is typically seen in individuals aged 10 to 35, and affects between 0.011% and 0.5% of the general population.

Conversion disorder can present with motor or sensory symptoms including any of the following:

Motor symptoms or deficits:

- Impaired coordination or balance

- Weakness/paralysis of a limb or the entire body (hysterical paralysis or motor conversion disorders)

- Impairment or loss of speech (hysterical aphonia)

- Difficulty swallowing (dysphagia) or a sensation of a lump in the throat

- Urinary retention

- Psychogenic non-epileptic seizures or convulsions

- Persistent dystonia

- Tremor, myoclonus or other movement disorders

- Gait problems (astasia-abasia)

- Loss of consciousness (fainting)

Sensory symptoms or deficits:

- Impaired vision (hysterical blindness), double vision

- Impaired hearing (deafness)

- Loss or disturbance of touch or pain sensation

Conversion symptoms typically do not conform to known anatomical pathways and physiological mechanisms. It has sometimes been stated that the presenting symptoms tend to reflect the patient's own understanding of anatomy and that the less medical knowledge a person has, the more implausible are the presenting symptoms. However, no systematic studies have yet been performed to substantiate this statement.

Diffuse anxiety is stimulated by a minor catalyst and may persist long after the catalyst disappears.

In the DSM-5 the disorder has been renamed somatic symptom disorder (SSD), and includes SSD with predominantly somatic complaints (previously referred to as somatization disorder), and SSD with pain features (previously known as pain disorder).

Schizoaffective disorder is defined by "mood disorder-free psychosis" in the context of a long-term psychotic and mood disorder. Psychosis must meet criterion A for schizophrenia which may include delusions, hallucinations, disorganized speech, thinking or behavior and negative symptoms. Both delusions and hallucinations are classic symptoms of psychosis. Delusions are false beliefs which are strongly held despite evidence to the contrary. Beliefs should not be considered delusional if they are in keeping with cultural beliefs. Delusional beliefs may or may not reflect mood symptoms (for example, someone experiencing depression may or may not experience delusions of guilt). Hallucinations are disturbances in perception involving any of the five senses, although auditory hallucinations (or "hearing voices") are the most common. A lack of responsiveness or negative symptoms include alogia (lack of spontaneous speech), blunted affect (reduced intensity of outward emotional expression), avolition (loss of motivation), and anhedonia (inability to experience pleasure). Negative symptoms can be more lasting and more debilitating than positive symptoms of psychosis.

Mood symptoms are of mania, hypomania, mixed episode, or depression, and tend to be episodic rather than continuous. A mixed episode represents a combination of symptoms of mania and depression at the same time. Symptoms of mania include elevated or irritable mood, grandiosity (inflated self-esteem), agitation, risk-taking behavior, decreased need for sleep, poor concentration, rapid speech, and racing thoughts. Symptoms of depression include low mood, apathy, changes in appetite or weight, disturbances in sleep, changes in motor activity, fatigue, guilt or feelings of worthlessness, and suicidal thinking.

The main symptoms of paraphrenia are paranoid delusions and hallucinations. The delusions often involve the individual being the subject of persecution, although they can also be erotic, hypochondriacal, or grandiose in nature. The majority of hallucinations associated with paraphrenia are auditory, with 75% of patients reporting such an experience; however, visual, tactile, and olfactory hallucinations have also been reported. The paranoia and hallucinations can combine in the form of “threatening or accusatory voices coming from neighbouring houses [and] are frequently reported by the patients as disturbing and undeserved". Patients also present with a lack of symptoms commonly found in other mental disorders similar to paraphrenia. There is no significant deterioration of intellect, personality, or habits and patients often remain clean and mostly self-sufficient. Patients also remain oriented well in time and space.

Paraphrenia is different from schizophrenia because, while both disorders result in delusions and hallucinations, individuals with schizophrenia exhibit changes and deterioration of personality whereas individuals with paraphrenia maintain a well-preserved personality and affective response.

Individuals with schizophrenia may experience hallucinations (most reported are hearing voices), delusions (often bizarre or persecutory in nature), and disorganized thinking and speech. The last may range from loss of train of thought, to sentences only loosely connected in meaning, to speech that is not understandable known as word salad. Social withdrawal, sloppiness of dress and hygiene, and loss of motivation and judgment are all common in schizophrenia.

Distortions of self-experience such as feeling as if one's thoughts or feelings are not really one's own to believing thoughts are being inserted into one's mind, sometimes termed passivity phenomena, are also common. There is often an observable pattern of emotional difficulty, for example lack of responsiveness. Impairment in social cognition is associated with schizophrenia, as are symptoms of paranoia. Social isolation commonly occurs. Difficulties in working and long-term memory, attention, executive functioning, and speed of processing also commonly occur. In one uncommon subtype, the person may be largely mute, remain motionless in bizarre postures, or exhibit purposeless agitation, all signs of catatonia. People with schizophrenia often find facial emotion perception to be difficult. It is unclear if the phenomenon called "thought blocking", where a talking person suddenly becomes silent for a few seconds to minutes, occurs in schizophrenia.

About 30 to 50 percent of people with schizophrenia fail to accept that they have an illness or comply with their recommended treatment. Treatment may have some effect on insight.

People with schizophrenia may have a high rate of irritable bowel syndrome but they often do not mention it unless specifically asked. Psychogenic polydipsia, or excessive fluid intake in the absence of physiological reasons to drink, is relatively common in people with schizophrenia.

In ICD-10, the latest version of the International Statistical Classification of Diseases and Related Health Problems, somatization syndrome is described as:

ICD-10 also includes the following subgroups of somatization syndrome:

- Undifferentiated somatoform disorder

- Hypochondriasis

- Somatoform autonomic dysfunction

- Persistent somatoform pain disorder

- Other somatoform disorders, such ones predominated by dysmenorrhoea, dysphagia, pruritus and torticollis

- Somatoform disorder, unspecified

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.

Schizophrenia is often described in terms of positive and negative (or deficit) symptoms. "Positive symptoms" are those that most individuals do not normally experience, but are present in people with schizophrenia. They can include delusions, disordered thoughts and speech, and tactile, auditory, visual, olfactory and gustatory hallucinations, typically regarded as manifestations of psychosis. Hallucinations are also typically related to the content of the delusional theme. Positive symptoms generally respond well to medication.

"Negative symptoms" are deficits of normal emotional responses or of other thought processes, and are less responsive to medication. They commonly include flat expressions or little emotion, poverty of speech, inability to experience pleasure, lack of desire to form relationships, and lack of motivation. Negative symptoms appear to contribute more to poor quality of life, functional ability, and the burden on others than positive symptoms do. People with greater negative symptoms often have a history of poor adjustment before the onset of illness, and response to medication is often limited.

The validity of the positive and negative construct has been challenged by factor analysis studies observing a three dimension grouping of symptoms. While different terminology is used, a dimension for hallucinations, a dimension for disorganization, and a dimension for negative symptoms are usually described.

A mental disorder, also called a mental illness or psychiatric disorder, is a behavioral or mental pattern that causes significant distress or impairment of personal functioning. Such features may be persistent, relapsing and remitting, or occur as a single episode. Many disorders have been described, with signs and symptoms that vary widely between specific disorders. Such disorders may be diagnosed by a mental health professional.

The causes of mental disorders are often unclear. Theories may incorporate findings from a range of fields. Mental disorders are usually defined by a combination of how a person behaves, feels, perceives, or thinks. This may be associated with particular regions or functions of the brain, often in a social context. A mental disorder is one aspect of mental health. Cultural and religious beliefs, as well as social norms, should be taken into account when making a diagnosis.

Services are based in psychiatric hospitals or in the community, and assessments are carried out by psychiatrists, psychologists, and clinical social workers, using various methods but often relying on observation and questioning. Treatments are provided by various mental health professionals. Psychotherapy and psychiatric medication are two major treatment options. Other treatments include social interventions, peer support, and self-help. In a minority of cases there might be involuntary detention or treatment. Prevention programs have been shown to reduce depression.

Common mental disorders include depression, which affects about 400 million, dementia which affects about 35 million, and schizophrenia, which affects about 21 million people globally. Stigma and discrimination can add to the suffering and disability associated with mental disorders, leading to various social movements attempting to increase understanding and challenge social exclusion.

Dissociative disorder not otherwise specified (DDNOS) is a mental health diagnosis for pathological dissociation that matches the DSM-5 criteria for a dissociative disorder, but does not fit the full criteria for any of the specifically identified subtypes, which include dissociative identity disorder, dissociative amnesia, and depersonalization/derealization disorder. The International Statistical Classification of Diseases and Related Health Problems (ICD-10) refers to the diagnosis as "Other dissociative and conversion disorders".

Examples of DDNOS include chronic and recurrent syndromes of mixed dissociative symptoms, identity disturbance due to prolonged and intense coercive persuasion, disorders similar to dissociative identity disorder, acute dissociative reactions to stressful events, and dissociative trance.

DDNOS is the most common dissociative disorder and is diagnosed in 40% of dissociative disorder cases. It is often co-morbid with other mental illnesses such as complex posttraumatic stress disorder, major depressive disorder, generalized anxiety disorder, personality disorders, substance abuse disorders and eating disorders.

Because the nature of acute schizophrenia is similar to depression, it is difficult to differentiate normal levels of depression in patients with schizophrenia from depressive levels in post-schizophrenic depression. "Prominent subjectively low mood, suggesting depression, and prominent blunting of affect, suggesting negative symptoms, are the two features which are most helpful in differentiating [schizophrenia and depression]." A number of researchers believe that depression is actually a symptom of schizophrenia that has been hidden by the psychosis. However, symptoms usually arise after the first psychotic episodes if they will arise at all. Officially, diagnosing post-schizophrenia depression in a patient requires for the patient to be experiencing a depressive episode of either short or long term following the overcoming of schizophrenia. The patient must still demonstrate some schizophrenic symptoms but those symptoms must no longer be the focus of the illness. Typically, the depressive symptoms are not severe enough to be classified as a severe depressive episode. Formally, diagnosis entails the patient having had schizophrenia within the past year, a number of schizophrenic symptoms, and depression being present for two weeks or more. Mild schizophrenic signs may be withdrawing socially, agitation or hostility, and irregular sleep such as in the case of insomnia and hypersomnia.

The ICD-10 includes a diagnostic guideline for the wide group of personality and behavioural disorders. However, every disorder has its own diagnostic criteria. In case of the organic personality disorder, patient has to show at least three of the following diagnostic criteria over a six or more months period. organic personality disorder is associated with a large variety of symptoms, such as deficits in cognitive function, dysfunctional behaviours, psychosis, neurosis, emotional changes, alterations in expression function and irritability. Patients with organic personality disorder can present emotional lability that means their emotional expressions are unstable and fluctuating. In addition, patients show reduction in ability of perseverance with their goals and they express disinhibited behaviours, which are characterised by inappropriate sexual and antisocial actions. For instance, patients can show dissocial behaviours, like stealing. Moreover, according to diagnostic guideline of ICD-10, patients can suffer from cognitive disturbances and they present signs of suspiciousness and paranoid ideas. Additionally, patients may present alteration in process of language production that means there are changes in language rate and flow. Furthermore, patients may show changes in their sexual preference and hyposexuality symptoms.

Another common feature of personality of patients with organic personality disorder is their dysfunctional and maladaptive behaviour that causes serious problems in these patients, because they face problems with pursuit and achievement of their goals. It is worth to be mentioned that patients with organic personality disorder express a feeling of unreasonable satisfaction and euphoria. Also, the patients show aggressive behaviours sometimes and these serious dysfunctions in their behaviour can have effects on their life and their relationships with other people. Specifically patients show intense signs of anger and aggression because of their inability to handle their impulses. The type of this aggression is called "impulsive aggression". Furthermore, it is worth to be mentioned that the pattern of organic personality disorder presents some similarities with pattern of temporal lobe epilepsy (TLE). Specifically patients who suffer from this chronic disorder type of epilepsy, express aggressive behaviours, likewise it happens to patients with organic personality disorder. Another similar symptom between Temporal lobe epilepsy and organic personality disorder is the epileptic seizure. The symptom of epileptic seizure has influence on patients' personality that means it causes behavioural alterations". The Temporal lobe epilepsy (TLE) is associated with the hyperexcitability of the medial temporal lobe (MTL) of patients. Finally, patients with organic personality disorder may present similar symptoms with patients, who suffer from the Huntington's disease as well. The symptoms of apathy and irritability are common between these two groups of patients.

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.

Schizoaffective disorder (SZA, SZD or SAD) is a mental disorder characterized by abnormal thought processes and deregulated emotions. The diagnosis is made when the person has features of both schizophrenia and a mood disorder—either bipolar disorder or depression—but does not strictly meet diagnostic criteria for either alone. The bipolar type is distinguished by symptoms of mania, hypomania, or mixed episode; the depressive type by symptoms of depression only. Common symptoms of the disorder include hallucinations, paranoid delusions, and disorganized speech and thinking. The onset of symptoms usually begins in young adulthood, currently with an uncertain lifetime prevalence because the disorder was redefined, but DSM-IV prevalence estimates were less than 1 percent of the population, in the range of 0.5 to 0.8 percent. Diagnosis is based on observed behavior and the person's reported experiences.

Genetics, neurobiology, early and current environment, behavioral, social, and experiential components appear to be important contributory factors; some recreational and prescription drugs may cause or worsen symptoms. No single isolated organic cause has been found, but extensive evidence exists for abnormalities in the metabolism of tetrahydrobiopterin (BH4), dopamine, and glutamic acid in people with schizophrenia, psychotic mood disorders, and schizoaffective disorder. People with schizoaffective disorder are likely to have co-occurring conditions, including anxiety disorders and substance use disorder. Social problems such as long-term unemployment, poverty and homelessness are common. The average life expectancy of people with the disorder is shorter than those without it, due to increased physical health problems from an absence of health promoting behaviors such as a sedentary lifestyle, and a higher suicide rate.

The mainstay of current treatment is antipsychotic medication combined with mood stabilizer medication or antidepressant medication, or both. There is growing concern by some researchers that antidepressants may increase psychosis, mania, and long-term mood episode cycling in the disorder. When there is risk to self or others, usually early in treatment, hospitalization may be necessary. Psychiatric rehabilitation, psychotherapy, and vocational rehabilitation are very important for recovery of higher psychosocial function. As a group, people with schizoaffective disorder diagnosed using DSM-IV and criteria have a better outcome than people with schizophrenia, but have variable individual psychosocial functional outcomes compared to people with mood disorders, from worse to the same. Outcomes for people with DSM-5 diagnosed schizoaffective disorder depend on data from prospective cohort studies, which haven't been completed yet.

In DSM-5 and ICD-10, schizoaffective disorder is in the same diagnostic class as schizophrenia, but not in the same class as mood disorders. The diagnosis was introduced in 1933, and its definition was slightly changed in the DSM-5, published in May 2013, because the DSM-IV schizoaffective disorder definition leads to excessive misdiagnosis. The changes made to the schizoaffective disorder definition were intended to make the DSM-5 diagnosis more consistent (or reliable), and to substantially reduce the use of the diagnosis. Additionally, the DSM-5 schizoaffective disorder diagnosis can no longer be used for first episode psychosis.

As it has already been mentioned, the organic personality disorder is included in a wide group of personality and behavioural disorders. This mental health disorder can be caused by disease, brain damages or dysfunctions in specific brain areas in frontal lobe. The most common reason for this profound change in personality is the traumatic brain injury (TBI). Children, whose brain areas have injured or damaged, may present Attention Deficit Hyperactivity Disorder (ADHD), oppositional defiant disorder (ODD) and organic personality disorder. Moreover, this disorder is characterised as "frontal lobe syndrome". This characteristic name shows that the organic personality disorder can usually be caused by lesions in three brain areas of frontal lobe. Specifically, the symptoms of organic personality disorder can also be caused by traumatic brain injuries in orbitofrontal cortex, anterior cingulate cortex and dorsolateral prefrontal cortex. It is worth to be mentioned that organic personality disorder may also be caused by lesions in other circumscribed brain areas.

A mental breakdown (also known as a nervous breakdown) is an acute, time-limited mental disorder that manifests primarily as severe stress-induced depression, anxiety, or dissociation in a previously functional individual, to the extent that they are no longer able to function on a day-to-day basis until the disorder is resolved. A nervous breakdown is defined by its temporary nature, and often closely tied to psychological burnout, severe overwork, sleep deprivation, and similar stressors, which may combine to temporarily overwhelm an individual with otherwise sound mental functions.

Paraphrenia (from – beside, near + φρήν – intellect, mind) is a mental disorder characterized by an organized system of paranoid delusions with or without hallucinations (the positive symptoms of schizophrenia) without deterioration of intellect or personality (its negative symptom).

This disorder is also distinguished from schizophrenia by a lower hereditary occurrence, less premorbid maladjustment, and a slower rate of progression. Onset of symptoms generally occurs later in life, near the age of 60. The prevalence of the disorder among the elderly is between 0.1 and 4%

Paraphrenia is not included in the DSM-5; psychiatrists often diagnose patients presenting with paraphrenia as having atypical psychoses, delusional disorder, psychoses not otherwise specified, schizoaffective disorders, and persistent persecutory states of older adults. Recently, mental health professionals have also been classifying paraphrenia as very late-onset schizophrenia-like psychosis.

In the Russian psychiatric manuals paraphrenia (or paraphrenic syndrome) is the last stage of development of paranoid schizophrenia. "Systematized paraphrenia" (with systematized delusions i. e. delusions with complex logical structure) and "expansive-paranoid paraphrenia" (with expansive/grandiose delusions and persecutory delusions) are the variants of paranoid schizophrenia (). You see sometimes "systematized paraphrenia" with delusional disorder ().

Somatic symptom disorders are a group of disorders, all of which fit the definition of physical symptoms similar to those observed in physical disease or injury for which there is no identifiable physical cause. As such, they are a diagnosis of exclusion. Somatic symptoms may be generalized in four major medical categories: neurological, cardiac, pain, and gastrointestinal somatic symptoms.

Post-schizophrenic depression is a "depressive episode arising in the aftermath of a schizophrenic illness where some low-level schizophrenic symptoms may still be present." Someone that suffers from post-schizophrenic depression experiences both symptoms of depression and can also continue showing mild symptoms of schizophrenia. Unfortunately, depression is a common symptom found in patients with schizophrenia and can fly under the radar for years before others become aware of its presence in a patient. However, very little research has been done on the subject, meaning there are few answers to how it should be systematically diagnosed, treated, or what course the illness will take. Some scientists would entirely deny the existence of post-schizophrenic depression, insisting it is a phase in schizophrenia as a whole. As of late, post-schizophrenic depression has become officially recognized as a syndrome and is considered a sub-type of schizophrenia.

Dissociative disorders (DD) are conditions that involve disruptions or breakdowns of memory, awareness, identity, or perception. People with dissociative disorders use dissociation, as a defence mechanism, pathologically and involuntarily. Dissociative disorders are sometimes triggered by psychological trauma, but may be preceded only by stress, psychoactive substances, or no identifiable trigger at all.

The dissociative disorders listed in the American Psychiatric Association's DSM-5 are as follows:

- Dissociative identity disorder (formerly multiple personality disorder): the alternation of two or more distinct personality states with impaired recall among personality states. In extreme cases, the host personality is unaware of the other, alternating personalities; however, the alternate personalities can be aware of all the existing personalities. This category now includes the old derealization disorder category.

- Dissociative amnesia (formerly psychogenic amnesia): the temporary loss of recall memory, specifically episodic memory, due to a traumatic or stressful event. It is considered the most common dissociative disorder amongst those documented. This disorder can occur abruptly or gradually and may last minutes to years depending on the severity of the trauma and the patient.

- Dissociative fugue (formerly psychogenic fugue) is now subsumed under the dissociative amnesia category. It is described as reversible amnesia for personal identity, usually involving unplanned travel or wandering, sometimes accompanied by the establishment of a new identity. This state is typically associated with stressful life circumstances and can be short or lengthy.

- Depersonalization disorder: periods of detachment from self or surrounding which may be experienced as "unreal" (lacking in control of or "outside" self) while retaining awareness that this is only a feeling and not a reality.

- The old category of dissociative disorder not otherwise specified is now split into two: Other specified dissociative disorder, and unspecified dissociative disorder. These categories are used for forms of pathological dissociation that do not fully meet the criteria of the other specified dissociative disorders, or if the correct category has not been determined.

Both dissociative amnesia and dissociative fugue usually emerge in adulthood and rarely occur after the age of 50. The ICD-10 classifies conversion disorder as a dissociative disorder while the DSM-IV classifies it as a somatoform disorder.