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.

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

- hallucinations

- delusions

- catatonia

- thought disorder.

Impairments in social cognition also occur.

Symptoms of psychotic breaks vary greatly, usually depending on the circumstances of diagnosis or any contributary substance ingested. Symptoms can range from harmless, sometimes unnoticed delusions, to violent outbursts and major depression. The sufferer may also be unable to distinguish reality from fantasy (for example, believing that a dream really happened or experiencing hallucinations that appear to be real). When a bipolar disorder is involved: crying, grandiosity, insomnia, irritability, and persecutory delusions may all or severally manifest themselves as symptoms.

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.

In the ICD-10, Bouffée délirante is classified as a subtype of either Acute polymorphic psychotic disorder without symptoms of schizophrenia (F23.0) or Acute polymorphic psychotic disorder with symptoms of schizophrenia (F23.1).

"Bouffée délirante" literally means a "delirious flash".

Though less common than stimulant psychosis, stimulants such as cocaine and amphetamines as well as the dissociative drug phencyclidine (PCP, angel dust) may also cause a theorized severe and life-threatening condition known as excited delirium. This condition manifests as a combination of delirium, psychomotor agitation, anxiety, delusions, hallucinations, speech disturbances, disorientation, violent and bizarre behavior, insensitivity to pain, elevated body temperature, and superhuman strength. Despite some superficial similarities in presentation excited delirium is a distinct (and more serious) condition than stimulant psychosis. The existence of excited delirium is currently debated.

A "manic episode" is defined in the American Psychiatric Association's diagnostic manual as a "distinct period of abnormally and persistently elevated, expansive, or irritable mood and abnormally and persistently increased activity or energy, lasting at least 1 week and present most of the day, nearly every day (or any duration if hospitalization is necessary)," where the mood is not caused by drugs/medication or a medical illness (e.g., hyperthyroidism), and (a) is causing obvious difficulties at work or in social relationships and activities, or (b) requires admission to hospital to protect the person or others, or (c) the person is suffering psychosis.

To be classed as a manic episode, while the disturbed mood and an increase in goal directed activity or energy is present at least three (or four if only irritability is present) of the following must have been consistently present:

1. Inflated self-esteem or grandiosity.

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

3. More talkative than usual or pressure to keep talking.

4. Flights of ideas or subjective experience that thoughts are racing.

5. Increase in goal directed activity, or psychomotor acceleration.

6. Distractibility (too easily drawn to unimportant or irrelevant external stimuli).

7. Excessive involvement in activities with a high likelihood of painful consequences.(e.g., extravagant shopping, improbable commercial schemes, hypersexuality).

Though the activities one participates in while in a manic state are not "always" negative, those with the potential to have negative outcomes are far more likely.

If the person is concurrently depressed, they are said to be having a mixed episode.

The World Health Organization's classification system defines "a manic episode" as one where mood is higher than the person's situation warrants and may vary from relaxed high spirits to barely controllable exuberance, accompanied by hyperactivity, a compulsion to speak, a reduced sleep requirement, difficulty sustaining attention and often increased distractibility. Frequently, confidence and self-esteem are excessively enlarged, and grand, extravagant ideas are expressed. Behavior that is out of character and risky, foolish or inappropriate may result from a loss of normal social restraint.

Some people also have physical symptoms, such as sweating, pacing, and weight loss. In full-blown mania, often the manic person will feel as though his or her goal(s) trump all else, that there are no consequences or that negative consequences would be minimal, and that they need not exercise restraint in the pursuit of what they are after. Hypomania is different, as it may cause little or no impairment in function. The hypomanic person's connection with the external world, and its standards of interaction, remain intact, although intensity of moods is heightened. But those who suffer from prolonged unresolved hypomania do run the risk of developing full mania, and indeed may cross that "line" without even realizing they have done so.

One of the most signature symptoms of mania (and to a lesser extent, hypomania) is what many have described as racing thoughts. These are usually instances in which the manic person is excessively distracted by objectively unimportant stimuli. This experience creates an absent-mindedness where the manic individual's thoughts totally preoccupy him or her, making him or her unable to keep track of time, or be aware of anything besides the flow of thoughts. Racing thoughts also interfere with the ability to fall asleep.

Manic states are always relative to the normal state of intensity of the afflicted individual; thus, already irritable patients may find themselves losing their tempers even more quickly and an academically gifted person may, during the hypomanic stage, adopt seemingly "genius" characteristics and an ability to perform and articulate at a level far beyond that which would be capable during euthymia. A very simple indicator of a manic state would be if a heretofore clinically depressed patient suddenly becomes inordinately energetic, cheerful, aggressive, or "over happy." Other, often less obvious, elements of mania include delusions (generally of either grandeur or persecution, according to whether the predominant mood is euphoric or irritable), hypersensitivity, hyper vigilance, hypersexuality, hyper-religiosity, hyperactivity and impulsivity, a compulsion to over explain, (typically accompanied by pressure of speech) grandiose schemes and ideas, and a decreased need for sleep (for example, feeling rested after only 3 or 4 hours of sleep); in the case of the latter, the eyes of such patients may both look and feel abnormally "wide" or "open," rarely blinking, and this often contributing to some clinicians’ erroneous belief that these patients are under the influence of a stimulant drug, when the patient, in fact, is either not on any mind-altering substances or is actually on a depressant drug, in a misguided attempt to ward off any undesirable manic symptoms. Individuals may also engage in out-of-character behavior during the episode, such as questionable business transactions, wasteful expenditures of money (e.g., spending sprees), risky sexual activity, abuse of recreational substances, excessive gambling, reckless behavior (as "speed driving" or daredevil activity), abnormal social interaction (as manifest via, for example, over familiarity and conversing with strangers), or highly vocal arguments. These behaviours may increase stress in personal relationships, lead to problems at work and increase the risk of altercations with law enforcement. There is a high risk of impulsively taking part in activities potentially harmful to self and others.

Although "severely elevated mood" sounds somewhat desirable and enjoyable, the experience of mania is ultimately often quite unpleasant and sometimes disturbing, if not frightening, for the person involved and for those close to them, and it may lead to impulsive behaviour that may later be regretted. It can also often be complicated by the sufferer's lack of judgment and insight regarding periods of exacerbation of characteristic states. Manic patients are frequently grandiose, obsessive, impulsive, irritable, belligerent, and frequently deny anything is wrong with them. Because mania frequently encourages high energy and decreased perception of need or ability to sleep, within a few days of a manic cycle, sleep-deprived psychosis may appear, further complicating the ability to think clearly. Racing thoughts and misperceptions lead to frustration and decreased ability to communicate with others.

Mania may also, as earlier mentioned, be divided into three “stages.” Stage I corresponds with hypomania and may feature typical hypomanic characteristics, such as gregariousness and euphoria. In stages II and III mania, however, the patient may be extraordinarily irritable, psychotic or even delirious. These latter two stages are referred to as acute and delirious (or Bell’s), respectively.

Individuals experiencing religious delusions are preoccupied with religious subjects that are not within the expected beliefs for an individual's background, including culture, education, and known experiences of religion. These preoccupations are incongruous with the mood of the subject. Falling within the definition also are delusions arising in psychotic depression; however, these must present within a major depressive episode and be congruous with mood.

Researchers in a 2000 study found religious delusions to be unrelated to any specific set of diagnostic criteria, but correlated with demographic criteria, primarily age. In a comparative study sampling 313 patients, those with religious delusion were found to be aged older, and had been placed on a drug regime or started a treatment programme at an earlier stage. In the context of presentation, their global functioning was found to be worse than another group of patients without religious delusions. The first group also scored higher on the Scale for the Assessment of Positive Symptoms (SAPS), had a greater total on the Brief Psychiatric Rating Scale (BPRS), and were treated with a higher mean number of neuroleptic medications of differing types during their hospitalization.

Religious delusion was found in 2007 to strongly correlate with "temporolimbic overactivity". This is a condition where irregularities in the brain's limbic system may present as symptoms of paranoid schizophrenia.

In a 2010 study, Swiss psychiatrists found religious delusions with themes of spiritual persecution by malevolent spirit-entities, control exerted over the person by spirit-entities, delusional experience of sin and guilt, or delusions of grandeur.

Religious delusions have generally been found to be less stressful than other types of delusion. A study found adherents to new religious movements to have similar delusionary cognition, as rated by the Delusions Inventory, to a psychotic group, although the former reported feeling less distressed by their experiences than the latter.

A single manic episode, in the absence of secondary causes, (i.e., substance use disorder, pharmacologic, general medical condition) is sufficient to diagnose bipolar I disorder. Hypomania may be indicative of bipolar II disorder. Manic episodes are often complicated by delusions and/or hallucinations; should the psychotic features persist for a duration significantly longer than the episode of mania (two weeks or more), a diagnosis of schizoaffective disorder is more appropriate. Certain of "obsessive-compulsive spectrum" disorders as well as impulse control disorders share the name "mania," namely, kleptomania, pyromania, and trichotillomania. Despite the unfortunate association implied by the name, however, no connection exists between mania or bipolar disorder and these disorders.

B deficiency can also cause characteristics of mania and psychosis.

Hyperthyroidism can produce similar symptoms to those of mania, such as agitation, elevated mood, increased energy, hyperactivity, sleep disturbances and sometimes, especially in severe cases, psychosis.

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.

Bouffée délirante is a culture-bound syndrome in West Africa and Haiti of a sudden outburst of aggression, confusion and psychomotor excitement, possibly including visual or auditory hallucinations and paranoia.

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.

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.

A religious delusion is any delusion involving religious themes or subject matter. Though a small minority of psychologists have characterized all or nearly all religion as delusion, others focus solely on a denial of any spiritual cause of symptoms exhibited by a patient and look for other answers relating to a chemical imbalance in the brain, although there is actually no evidence of pathology in any psychiatric illness which means a diagnosis is made purely on opinions of professionals based on symptoms the person exhibits.

The disorder is characterized by a sudden onset of psychotic symptoms, which may include delusions, hallucinations, disorganized speech or behavior, or catatonic behavior. The symptoms must not be caused by schizophrenia, schizoaffective disorder, delusional disorder or mania in bipolar disorder. They must also not be caused by a drug (such as amphetamines) or medical condition (such as a brain tumor). The term bouffée délirante describes an acute nonaffective and nonschizophrenic psychotic disorder, which is largely similar to DSM-III-R and DSM-IV brief psychotic and schizophreniform disorders.

Symptoms generally last at least a day, but not more than a month, and there is an eventual return to full baseline functioning. It may occur in response to a significant stressor in one's life, or in other situations where a stressor is not apparent, including in the weeks following birth. In diagnosis, a careful distinction is considered for culturally appropriate behaviors, such as religious beliefs and activities. It is believed to be connected to or synonymous with a variety of culture-specific phenomena such as latah, koro, and amok.

There are three forms of brief psychotic disorder:

1. Brief psychotic disorder with a stressor, such as a trauma or death in the family.

2. Brief psychotic disorder without a stressor, there is no obvious stressor.

3. Brief psychotic disorder with postpartum onset. Usually occurs about four weeks after giving birth.

A psychotic break occurs when a person experiences an episode of acute primary psychosis, generally for the first time, though it may also be after a significant symptom-free period.

The article "Betwixt Life and Death: Case Studies of the Cotard Delusion" (1996) describes a contemporary case of Cotard delusion, which occurred in a Scotsman whose brain was damaged in a motorcycle accident:

The article "Recurrent Postictal Depression with Cotard Delusion" (2005) describes the case of a fourteen-year-old epileptic boy whose distorted perception of reality resulted from Cotard syndrome. His mental health history was of a boy expressing themes of death, chronic sadness, decreased physical activity in playtime, social withdrawal, and disturbed biological functions. About twice a year, the boy suffered episodes that lasted between three weeks and three months. In the course of each episode, he said that everyone and everything was dead (including trees), described himself as a dead body, and warned that the world would be destroyed within hours. Throughout the episode, the boy showed no response to pleasurable stimuli and had no interest in social activities.

Chronic abuse of methylphenidate can also lead to psychosis. Psychotic symptoms from methylphenidate can include hearing voices, visual hallucinations, urges to harm oneself, severe anxiety, mania, grandiosity, paranoid delusions, confusion, increased aggression, and irritability.

Schizophrenia is a mental disorder that is expressed in abnormal mental functions and disturbed behavior.

The signs and symptoms of childhood schizophrenia are nearly the same as adult-onset schizophrenia. Some of the earliest signs that a young child may develop schizophrenia are lags in language and motor development. Some children engage in activities such as flapping the arms or rocking, and may appear anxious, confused, or disruptive on a regular basis. Children may experience symptoms such as hallucinations, but these are often difficult to differentiate from just normal imagination or child play. It is often difficult for children to describe their hallucinations or delusions, making very early-onset schizophrenia especially difficult to diagnose in the earliest stages. The cognitive abilities of children with schizophrenia may also often be lacking, with 20% of patients showing borderline or full intellectual disability.

Very early-onset schizophrenia refers to onset before the age of thirteen. The prodromal phase, which precedes psychotic symptoms, is characterized by deterioration in school performance, social withdrawal, disorganized or unusual behavior, a decreased ability to perform daily activities, a deterioration in self-care skills, bizarre hygiene and eating behaviors, changes in affect, a lack of impulse control, hostility and aggression, and lethargy.

Auditory hallucinations are the most common "positive symptom" in children. Positive symptoms have come to mean psychopathological disorders that are actively expressed, such as delusions, hallucinations, thought disorder etc.). A child's auditory hallucinations may include voices that are conversing with each other or voices that are speaking directly to the children themselves. Many children with auditory hallucinations believe that if they do not listen to the voices, the voices will harm them or someone else. Tactile and visual hallucinations seem relatively rare. The children often attribute the hallucinatory voices to a variety of beings, including family members or other people, evil forces ("the Devil", "a witch", "a spirit"), animals, characters from horror movies (Bloody Mary, Freddy Krueger) and less clearly recognizable sources ("bad things," "the whispers"). Command auditory hallucinations (also known as imperative hallucinations) were common and experienced by more than ½ of the group in a research at the Bellevue Hospital Center's Children's Psychiatric Inpatient Unit. And voices repeat and repeat: "Kill somebody!", "Kill her, kill her!". Delusions are reported in more than half of children with schizophrenia, but they are usually less complex than those of adults. Delusions often connected with hallucinatory experiences.. In a research delusions were characterized as persecutory for the most part, but some children reported delusions of control. Many said they were being tortured by the beings causing their visual and auditory hallucinations, some thought that if they disobeying their voices would cause them harm.

Some degree of thought disorder was observed in a test group of children in Bellevue Hospital. They displayed illogicality, tangentialiry (a serious disturbance in the associative thought process), and loosening of associations.

Negative ("deficit") symptoms in schizophrenia reflect mental deficit states such as apathy and aboulia, avolition, flattened affect, asthenia etc.

This is described as a rare form of severe mental illness, with the following characteristics:

- Sudden onset in a previously asymptomatic person.

- Brief duration, with full recovery.

- Psychotic symptoms that can include confusion or hallucinations, mutism and stupor, delusions, or manic state. These are distinct from premenstrual tension, premenstrual syndrome, premenstrual (late luteal phase) depression or dysphoric disorder or menstrual mood disorder.

- Occurrence in rhythm with the menstrual cycle.

It shares clinical features with, and presents similarly to, postpartum psychosis. Researchers Deuchar and Brockington proposed that a sudden drop in levels of estrogen in the brain could be the trigger for both conditions.

The delusion of negation is the central symptom in Cotard's syndrome. The patient afflicted with this mental illness usually denies his or her existence, the existence of a certain body part, or the existence of a portion of their body. Cotard's syndrome exists in three stages: (i) Germination stage—the symptoms of psychotic depression and of hypochondria appear; (ii) Blooming stage—the full development of the syndrome and the delusions of negation; and (iii) Chronic stage—continued, severe delusions along with chronic psychiatric depression.

The Cotard syndrome withdraws the afflicted person from other people due to the neglect of their personal hygiene and physical health. The delusion of negation of self prevents the patient from making sense of external reality, which then produces a distorted view of the external world. Such a delusion of negation is usually found in the psychotic patient who also presents with schizophrenia. Although a diagnosis of Cotard's syndrome does not require the patient's having had hallucinations, the strong delusions of negation are comparable to those found in schizophrenic patients.

Command hallucinations are hallucinations in the form of commands; they can be auditory or inside of the person's mind and/or consciousness. The contents of the hallucinations can range from the innocuous to commands to cause harm to the self or others. Command hallucinations are often associated with schizophrenia. People experiencing command hallucinations may or may not comply with the hallucinated commands, depending on the circumstances. Compliance is more common for non-violent commands.

Command hallucinations are sometimes used in defense of a crime, often homicides. In essence, it is a voice that one hears and it tells the listener what to do. Sometimes the commands are quite benign directives such as "Stand up" or "Shut the door." Whether it is a command for something simple or something that is a threat, it is still considered a "command hallucination." Some helpful questions that can assist one in figuring out if he/she may be suffering from this include: "What are the voices telling you to do?", "When did your voices first start telling you to do things?", "Do you recognize the person who is telling you to harm yourself (or others)?", "Do you think you can resist doing what the voices are telling you to do?"

Phantosmia (olfactory hallucinations), smelling an odor that is not actually there, and parosmia (olfactory illusions), inhaling a real odor but perceiving it as different scent than remembered, are distortions to the sense of smell (olfactory system) that, in most cases, are not caused by anything serious and usually go away on their own in time. It can result from a range of conditions such as nasal infections, nasal polyps, dental problems, migraines, head injuries, seizures, strokes, or brain tumors. Environmental exposures are sometimes the cause as well, such as smoking, exposure to certain types of chemicals (e.g., insecticides or solvents), or radiation treatment for head or neck cancer. It can also be a symptom of certain mental disorders such as depression, bipolar disorder, intoxication or withdrawal from drugs and alcohol, or psychotic disorders (e.g., schizophrenia). The perceived odors are usually unpleasant and commonly described as smelling burned, foul spoiled, or rotten.

Brief reactive psychosis generally follows a recognisably traumatic life event like divorce or homelessness, but may be triggered by any subjective experience which appears catastrophic to the person affected.

Among such stressors are the death of a loved one, professional loss such as unexpectedly losing one's job or otherwise becoming unemployed, or serious adverse changes in the patient's personal life, such as the breakdown of their family through divorce, etc.

It must be emphasised that this is by no means an exhaustive list of stressful life events, because the events which trigger brief reactive psychosis tend, due to the individualistic nature of human psychology, to be extremely personalized. BRP may be the first breakdown for someone with a chronic psychiatric disorder but only time will tell whether the disorder will be brief or lifelong, whether BRP or a chronic condition that is controlled well enough by medication that symptoms do not return.

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.