Premorbidity refers to the state of functionality prior to the onset of a disease or illness. It is most often used in relation to psychological function (e.g. premorbid personality or premorbid intelligence), but can also be used in relation to other medical conditions (e.g. premorbid lung function or premorbid heart rate).

As affirmed by the "Diagnostic and Statistical Manual of Mental Disorders", fifth edition (DSM-V), the symptomology specifier "with mixed features" can be applied to manic episodes of bipolar I disorder, hypomanic episodes of either bipolar I disorder or bipolar II disorder, and depressive episodes of either bipolar disorder or major depressive disorder, with at least three concurrent features of the opposite polarity being present. As a result, the presence of "mixed features" are now recognized in patients with bipolar II disorder and major depression; as earlier noted, however, although it is customary to withhold a diagnosis of a bipolar disorder until a manic or hypomanic episode appears, the presence of such features in a depressed patient even with no history of discrete mania or hypomania is strongly suggestive of the disorder.

Two features of both mania or hypomania and depression may superficially overlap and even resemble each other, namely "an increase in goal-directed activity" (psychomotor acceleration) vs. psychomotor agitation and "flight of ideas" and "racing thoughts" vs. depressive rumination. Attending to the patient's experiences is very important. In the psychomotor agitation commonly seen in depression, the "nervous energy" is always overshadowed by a strong sense of exhaustion and manifests as purposeless movements (e.g., pacing, hand-wringing); in psychomotor acceleration, however, the excess in movement stems from an abundance of energy and is often channelled and purposeful. Likewise, in depressive rumination, the patient experiences the repetitive thoughts as heavy, leaden, and plodding; in psychic acceleration, however, (as seen in mania or hypomania) the thoughts move in a rapid progression, with many themes, rather than a singular one, being touched upon. Even when such experiences are accounted for on the basis of depression, the possibility does still exist, however, that the depressive episode may be complicated by other manic or hypomanic symptoms, in which case it is often prudent to attend to the patient's personal and family history (e.g., family history of bipolar disorder, early age of onset) to determine whether or not the patient has bipolar disorder.

People with psychosis normally have one or more of the following:

- hallucinations

- delusions

- catatonia

- thought disorder.

Impairments in social cognition also occur.

Mania is a distinct period of at least one week of elevated or irritable mood, which can range from euphoria to delirium, and those experiencing hypo- or mania may exhibit three or more of the following behaviors: speak in a rapid, uninterruptible manner, short attention span, racing thoughts, increased goal-oriented activities, agitation, or they may exhibit behaviors characterized as impulsive or high-risk, such as hypersexuality or excessive spending. To meet the definition for a manic episode, these behaviors must impair the individual's ability to socialize or work. If untreated, a manic episode usually lasts three to six months.

People with hypomania or mania may experience a decreased need of sleep, impaired judgment, and speak excessively and very rapidly. Manic individuals often have a history of substance abuse developed over years as a form of "self-medication". At the more extreme, a person in a full blown manic state can experience psychosis; a break with reality, a state in which thinking is affected along with mood. They may feel unstoppable, or as if they have been "chosen" and are on a "special mission", or have other grandiose or delusional ideas. This may lead to violent behavior and, sometimes, hospitalization in an inpatient psychiatric hospital. The severity of manic symptoms can be measured by rating scales such as the Young Mania Rating Scale, though questions remain about the reliability of these scales.

The onset of a manic or depressive episode is often foreshadowed by sleep disturbances. Mood changes, psychomotor and appetite changes, and an increase in anxiety can also occur up to three weeks before a manic episode develops.

A hallucination is defined as sensory perception in the absence of external stimuli. Hallucinations are different from illusions, or perceptual distortions, which are the misperception of external stimuli. Hallucinations may occur in any of the senses and take on almost any form, which may include simple sensations (such as lights, colors, tastes, and smells) to experiences such as seeing and interacting with fully formed animals and people, hearing voices, and having complex tactile sensations.

Auditory hallucinations, particularly experiences of hearing voices, are the most common and often prominent feature of psychosis. Hallucinated voices may talk about, or to, the person, and may involve several speakers with distinct personalities. Auditory hallucinations tend to be particularly distressing when they are derogatory, commanding or preoccupying. However, the experience of hearing voices need not always be a negative one. One research study has shown that the majority of people who hear voices are not in need of psychiatric help. The Hearing Voices Movement has subsequently been created to support voice hearers, regardless of whether they are considered to have a mental disorder or not.

Symptoms of the depressive phase of bipolar disorder include persistent feelings of sadness, irritability or anger, loss of interest in previously enjoyed activities, excessive or inappropriate guilt, hopelessness, sleeping too much or not enough, changes in appetite and/or weight, fatigue, problems concentrating, self-loathing or feelings of worthlessness, and thoughts of death or suicide. In severe cases, the individual may develop symptoms of psychosis, a condition also known as severe bipolar disorder with psychotic features. These symptoms include delusions and hallucinations. A major depressive episode persists for at least two weeks, and may result in suicide if left untreated.

The earlier the age of onset, the more likely the first few episodes are to be depressive. Since a diagnosis of bipolar disorder requires a manic or hypomanic episode, many affected individuals are initially misdiagnosed as having major depression and then incorrectly treated with prescribed antidepressants.

Traditionally, a mixed affective state, formerly known as a mixed-manic or mixed episode, has been defined as a state wherein features unique to both depression and mania—such as despair, fatigue, morbid or suicidal ideation; racing thoughts, pressure of activity, and heightened irritability—occur either simultaneously or in very short succession.

Previously, the diagnostic criteria for both a manic and depressive episode had to be met in a consistent and sustained fashion, with symptoms enduring for at least a week (or any duration if psychiatric hospitalization was required), thereby restricting the official acknowledgement of mixed affective states to only a minority of patients with bipolar I disorder. In current (DSM-V) nomenclature, however, a "mixed episode" no longer stands as an episode of illness unto itself; rather, the symptomology specifier "with mixed features" can be applied to any major affective episode (manic, hypomanic, or depressive), meaning that they are now officially recognized in patients with, in addition to bipolar I disorder, bipolar II disorder and, by convention, major depressive disorder; a depressive mixed state in a patient, however, even in the absence of discrete periods of mania or hypomania, effectively rules out unipolar depression. Although convention dictates diagnosing such patients with major depressive disorder, it is more appropriate to classify such a patient as having an "Other Specified Bipolar or Related Disorder" and certainly following up such patients in the long-term, to ascertain the eventual appearance of an episode of mania or hypomania (with or without mixed features), which would prompt diagnostic revision. In those uncommon cases wherein the diagnostic criteria for both a manic and depressive episode are met, constituting what were heretofore classified as "mixed episodes", such a patient would be diagnosed as having a "manic episode with mixed features", because of the substantial social and occupational dysfunction inherent in such a state.

Depressive mixed states occur when patients experience depression and non-euphoric, usually subsyndromal, hypomania at the same time. As mentioned previously, it is particularly difficult to diagnose BP-II when a patient is in this state.

In a mixed state, mood is depressed, but the following symptoms of hypomania present as well:

- Irritability

- Mental overactivity

- Behavioral overactivity

Mixed states are associated with greater levels of suicidality than non-mixed depression. Antidepressants may increase this risk.

Hypomania is the signature characteristic of Bipolar II disorder. It is a state characterized by euphoria and/or an irritable mood. In order for an episode to qualify as hypomanic, the individual must also present three or more of the below symptoms, and last at least four consecutive days and be present most of the day, nearly every day

- Inflated self-esteem or grandiosity.

- Decreased need for sleep (e.g., feels rested after only 3 hours of sleep).

- More talkative than usual or pressure to keep talking.

- Flight of ideas or subjective experience that thoughts are racing.

- Distractibility (i.e., attention too easily drawn to unimportant or irrelevant external stimuli), as reported or observed.

- Increase in goal-directed activity (either socially, at work or school, or sexually) or psychomotor agitation.

- Excessive involvement in activities that have a high potential for painful consequences (e.g., engaging in unrestrained buying sprees, sexual indiscretions, or foolish business investments).

It is important to distinguish between hypomania and mania. Mania is generally greater in severity and impairs function, sometimes leading to hospitalization and in the most severe cases, psychosis. In contrast, hypomania usually increases functioning. For this reason, it is not uncommon for hypomania to go unnoticed. Often it is not until individuals are in a depressive episode that they seek treatment, and even then their history of hypomania may go undiagnosed. Even though hypomania may increase functioning, episodes need to be treated because they may precipitate a depressive episode.

At risk mental state is the clinical presentation of those considered at risk of developing psychosis or schizophrenia. Such states were formerly considered treated as prodromes, emerging symptoms of psychosis, but this view is no longer prevalent as a prodromal period can not be confirmed unless the emergence of the condition has occurred.

The original specialist service for those with subclinical symptoms of psychosis was "The Pace Clinic" in Melbourne, Australia. Other clinics have since developed around the world.

There has been some considerable development of how the concept can be applied clinically.

Assessed during the structured interview developed by PACE.

Mild and major neurocognitive disorders are usually associated with but not restricted to the elderly. Unlike delirium, conditions under these disorders develop slowly and are characterized by memory loss. In addition to memory loss and cognitive impairment, other symptoms include aphasia, apraxia, agnosia, loss of abstract thought, behavioral/personality changes, and impaired judgment. There may also be behavioral disturbances including psychosis, mood, and agitation.

Mild and major neurocognitive disorders are differentiated based on the severity of their symptoms. Previously known as dementia, major neurocognitive disorder is characterized by significant cognitive decline and interference with independence, while mild neurocognitive disorder is characterized by moderate cognitive decline and does not interfere with independence. To be diagnosed, it must not be due to delirium or other mental disorder. They are also usually accompanied by another cognitive dysfunction. For non-reversible causes of dementia such as age, the slow decline of memory and cognition is lifelong. It can be diagnosed by screening tests such as the Mini Mental State Examination (MMSE).

Delirium develops rapidly over a short period of time and is characterized by a disturbance in cognition, manifested by confusion, excitement, disorientation, and a clouding of consciousness. Hallucinations and illusions are common, and some individuals may experience acute onset change of consciousness. It is a disorder that makes situational awareness and processing new information very difficult for those diagnosed. It usually has a high rate of onset ranging from minutes to hours and sometimes days, but it does not last for very long, only a few hours to weeks. Delirium can also be accompanied by a shift in attention, mood swings, violent or unordinary behaviors, and hallucinations. It can be caused by a preexisting medical condition. Delirium during a hospital stay can result in a longer stay and more risk of complications and long terms stays.

Research suggests that the severity of the delusions of grandeur is directly related to a higher self-esteem in individuals and inversely related to any individual’s severity of depression and negative self-evaluations. Lucas "et al." found that there is no significant gender difference in the establishment of grandiose delusion. However, there is a claim that ‘the particular component of Grandiose delusion’ may be variable across both genders. Also, it had been noted that the presence of GDs in people with at least grammar or high school education was greater than lesser educated persons. Similarly, the presence of grandiose delusions in individuals who are the eldest is greater than in individuals who are the youngest of their siblings.

According to the DSM-IV-TR diagnostic criteria for delusional disorders, grandiose-type symptoms include grossly exaggerated beliefs of:

- self-worth

- power

- knowledge

- identity

- exceptional relationship to a divinity or famous person.

For example, a patient who has fictitious beliefs about his or her power or authority may believe himself or herself to be a ruling monarch who deserves to be treated like royalty.

There are substantial differences in the degree of grandiosity linked with grandiose delusions in different patients. Some patients believe they are God, the Queen of England, a president's son, a famous rock star, and so on. Others are not as expansive and think they are skilled sports-persons or great inventors.

Major depression significantly affects a person's family and personal relationships, work or school life, sleeping and eating habits, and general health. Its impact on functioning and well-being has been compared to that of other chronic medical conditions such as diabetes.

A person having a major depressive episode usually exhibits a very low mood, which pervades all aspects of life, and an inability to experience pleasure in activities that were formerly enjoyed. Depressed people may be preoccupied with, or ruminate over, thoughts and feelings of worthlessness, inappropriate guilt or regret, helplessness, hopelessness, and self-hatred. In severe cases, depressed people may have symptoms of psychosis. These symptoms include delusions or, less commonly, hallucinations, usually unpleasant. Other symptoms of depression include poor concentration and memory (especially in those with melancholic or psychotic features), withdrawal from social situations and activities, reduced sex drive, irritability, and thoughts of death or suicide. Insomnia is common among the depressed. In the typical pattern, a person wakes very early and cannot get back to sleep. Hypersomnia, or oversleeping, can also happen. Some antidepressants may also cause insomnia due to their stimulating effect.

A depressed person may report multiple physical symptoms such as fatigue, headaches, or digestive problems; physical complaints are the most common presenting problem in developing countries, according to the World Health Organization's criteria for depression. Appetite often decreases, with resulting weight loss, although increased appetite and weight gain occasionally occur. Family and friends may notice that the person's behavior is either agitated or lethargic. Older depressed people may have cognitive symptoms of recent onset, such as forgetfulness, and a more noticeable slowing of movements. Depression often coexists with physical disorders common among the elderly, such as stroke, other cardiovascular diseases, Parkinson's disease, and chronic obstructive pulmonary disease.

Depressed children may often display an irritable mood rather than a depressed mood, and show varying symptoms depending on age and situation. Most lose interest in school and show a decline in academic performance. They may be described as clingy, demanding, dependent, or insecure. Diagnosis may be delayed or missed when symptoms are interpreted as normal moodiness.

Chronic hallucinatory psychosis is a psychosis subtype, classified under "Other nonorganic psychosis" by the . Other abnormal mental symptoms in the early stages are, as a rule, absent. The patient is most usually quiet and orderly, with a good memory.

It has often been a matter of the greatest difficulty to decide under which heading of the recognized classifications individual members of this group should be placed. As the hallucinations give rise to slight depression, some might possibly be included under melancholia. In others, paranoia may develop. Others, again, might be swept into the widespread net of dementia praecox. This state of affairs cannot be regarded as satisfactory, for they are not truly cases of melancholia, paranoia, dementia praecox or any other described affection.

This disease, as its name suggests, is a hallucinatory case, for it is its main feature. These may be of all senses, but auditory hallucinations are the most prominent. At the beginning, the patient may realize that the hallucination is a morbid phenomenon and unaccountable. They may claim to hear a "voice" speaking, though there is no one in the flesh actually doing so. Such a state of affairs may last for years and possibly, though rarely, for life, and the subject would not be deemed insane in the ordinary sense of the word.

It's probable, however, that this condition forms the first stage of the illness, which eventually develops on definite lines. What usually happens is the patient seeks an explanation for the hallucinations. As none is forthcoming he/she tries to account for their presence and the result is a delusion, and, most frequently, a delusion of persecution. Also, it needs to be noted that the delusion is a comparatively late arrival and is the logical result of the hallucinations.

Oneirophenia and schizophrenia are often confused although there are distinct differences between the conditions. Oneirophrenia has some of the characteristics of simple schizophrenia, such as a confusional state and clouding of consciousness, but without presenting the dissociative symptoms which are typical of that disorder. Oneiophrenia often begins with the inability to focus on things while schizophrenia frequently starts with a traumatic event. Persons affected by oneirophrenia have a feeling of dream-like derealization which, in its extreme form, may progress to delusions and hallucinations. Therefore, it is considered a schizophrenia-like acute form of psychosis which remits in about 60% of cases within a period of two years. It is estimated that 50% or more of schizophrenic patients present oneirophrenia at least once.

Depression is a state of a low mood and aversion to activity that can affect a person's thoughts, behavior, feelings, and sense of well-being. A depressed mood is a normal temporary reaction to life events such as loss of a loved one. It is also a symptom of some physical diseases and a side effect of some drugs and medical treatments. Depressed mood is also a symptom of some mood disorders such as major depressive disorder or dysthymia.

People with a depressed mood may be notably sad, anxious, or empty; they may also feel notably hopeless, helpless, dejected, or worthless. Other symptoms expressed may include senses of guilt, irritability, or anger. Further feelings expressed by these individuals may include feeling ashamed or an expressed restlessness. These individuals may notably lose interest in activities that they once considered pleasurable to family and friends or otherwise experience either a loss of appetite or overeating. Experiencing problems concentrating, remembering general facts or details, otherwise making decisions or experiencing relationship difficulties may also be notable factors in these individuals' depression and may also lead to their attempting or actually dying by suicide.

Expressed insomnia, excessive sleeping, fatigue, and vocalizing general aches, pains, and digestive problems and a reduced energy may also be present in individuals experiencing depression.

The DSM-IV-TR recognizes five further subtypes of MDD, called "specifiers", in addition to noting the length, severity and presence of psychotic features:

- Melancholic depression is characterized by a loss of pleasure in most or all activities, a failure of reactivity to pleasurable stimuli, a quality of depressed mood more pronounced than that of grief or loss, a worsening of symptoms in the morning hours, early-morning waking, psychomotor retardation, excessive weight loss (not to be confused with anorexia nervosa), or excessive guilt.

- Atypical depression is characterized by mood reactivity (paradoxical anhedonia) and positivity, significant weight gain or increased appetite (comfort eating), excessive sleep or sleepiness (hypersomnia), a sensation of heaviness in limbs known as leaden paralysis, and significant social impairment as a consequence of hypersensitivity to perceived interpersonal rejection.

- Catatonic depression is a rare and severe form of major depression involving disturbances of motor behavior and other symptoms. Here, the person is mute and almost stuporous, and either remains immobile or exhibits purposeless or even bizarre movements. Catatonic symptoms also occur in schizophrenia or in manic episodes, or may be caused by neuroleptic malignant syndrome.

- Postpartum depression, or mental and behavioral disorders associated with the , not elsewhere classified, refers to the intense, sustained and sometimes disabling depression experienced by women after giving birth. Postpartum depression has an incidence rate of 10–15% among new mothers. The DSM-IV mandates that, in order to qualify as postpartum depression, onset occur within one month of delivery. It has been said that postpartum depression can last as long as three months.

- Seasonal affective disorder (SAD) is a form of depression in which depressive episodes come on in the autumn or winter, and resolve in spring. The diagnosis is made if at least two episodes have occurred in colder months with none at other times, over a two-year period or longer.

Oneirophrenia is often described as a dream-like state that can lead to hallucinations and confusion. Feelings and emotions are often disturbed but information from the senses is left intact separating it from true schizophrenia.

Although non-specific concepts of madness have been around for several thousand years, the psychiatrist and philosopher Karl Jaspers was the first to define the three main criteria for a belief to be considered delusional in his 1913 book "General Psychopathology". These criteria are:

- certainty (held with absolute conviction)

- incorrigibility (not changeable by compelling counterargument or proof to the contrary)

- impossibility or falsity of content (implausible, bizarre, or patently untrue)

Furthermore, when a false belief involves a value judgment, it is only considered a delusion if it is so extreme that it cannot be, or never can be proven true. For example: a man claiming that he flew into the sun and flew back home. This would be considered a delusion, unless he were speaking figuratively, or if the belief had a cultural or religious source.

A delusion is a mistaken belief that is held with strong conviction even when presented with superior evidence to the contrary. As a pathology, it is distinct from a belief based on false or incomplete information, confabulation, dogma, illusion, or some other misleading effects of perception.

Delusions typically occur in the context of neurological or psychiatric disease, although they are not tied to any particular disorder and have been found to occur in the context of many pathological states (both physical and mental). However, they are of particular diagnostic importance in psychotic disorders including schizophrenia, paraphrenia, manic episodes of bipolar disorder, and psychotic depression.

In the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR), paranoid, schizoid, and schizotypal personality disorders may be diagnosed as conditions "premorbid" to the onset of schizophrenia.

Recurrent brief depression (RBD) defines a mental disorder characterized by intermittent depressive episodes, not related to menstrual cycles in women, occurring between approximately 6-12 times per year, over at least one year or more fulfilling the diagnostic criteria for major depressive episodes (DSM-IV and ICD-10) except for duration which in RBD is less than 14 days, typically 2–4 days. Despite the short duration of the depressive episodes, such episodes are severe and suicidal ideation and impaired function is rather common. The majority of patients with RBD also report symptoms of anxiety and increased irritability. Hypersomnia is also rather frequent. About 1/2 of patients fulfilling diagnostic criteria for RBD may have additional short episodes of brief hypomania which is a severity marker of RBD. RBD may be the only mental disorder present, but RBD may also occur as part of a history of recurrent major depressive episodes or bipolar disorders. RBD is also seen among some patients with personality disorders.

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.