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

- hallucinations

- delusions

- catatonia

- thought disorder.

Impairments in social cognition also occur.

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 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.

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.

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.

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 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.

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.

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.

Schizophreniform disorder is a type of mental illness that is characterized by psychosis and closely related to schizophrenia. Both schizophrenia and schizophreniform disorder, as defined by the "Diagnostic and Statistical Manual of Mental Disorders" (DSM-IV-TR), have the same symptoms and essential features except for two differences: the level of functional impairment and the duration of symptoms. Impairment in social, occupational, or academic functioning is usually present in schizophrenia, particularly near the time of first diagnosis, but such impairment may or may not be present in schizophreniform disorder. In schizophreniform disorder, the symptoms (including prodromal, active, and residual phases) must last at least 1 month but not more than 6 months, while in schizophrenia the symptoms must be present for a minimum of 6 months.

If the symptoms have persisted for at least one month, a provisional diagnosis of schizophreniform disorder can be made while waiting to see if recovery occurs. If the symptoms resolve within 6 months of onset, the provisional qualifier is removed from the diagnosis. However, if the symptoms persist for 6 months or more, the diagnosis of schizophreniform disorder must be revised. The diagnosis of brief psychotic disorder may be considered when the duration of symptoms is less than one month.

The main symptoms of both schizophreniform disorder and schizophrenia may include:

- delusions,

- hallucinations,

- disorganized speech resulting from formal thought disorder,

- disorganized or catatonic behavior, and negative symptoms, such as

- an inability to feel a range of emotions (flat affect),

- an inability to experience pleasure (anhedonia),

- impaired or decreased speech (aphasia),

- a lack of desire to form relationships (asociality), and

- a lack of motivation (avolition).

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".

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.

The following specifiers for schizophreniform disorder may be used to indicate the presence or absence of features that may be associated with a better prognosis:

- With Good Prognostic Features, used if at least two of the following features are present:

- Onset of prominent psychotic symptoms within 4 weeks of the first noticeable change in usual behavior or functioning

- Confusion or perplexity at the height of the psychotic episode

- Good premorbid social and occupational functioning

- Absence of blunted or flat affect

- Without Good Prognostic Features, used if two or more of the above features have not been present.

The presence of negative symptoms and poor eye contact both appear to be prognostic of a poor outcome. Many of the anatomic and functional changes seen in the brains of patients with schizophrenia also occur in patients with schizophreniform disorder. However, at present there is no consensus among scientists regarding whether or not ventricular enlargement, which is a poor prognostic factor in schizophrenia, has any prognostic value in patients with schizophreniform disorder. According to the American Psychiatric Association, approximately two-thirds of patients diagnosed with "provisional" schizophreniform disorder are subsequently diagnosed with schizophrenia; the remaining keep a diagnosis of schizophreniform disorder.

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.

Symptoms usually begin suddenly in the first two weeks after delivery, sometimes in the first two to three days after giving birth. Symptoms vary and can change quickly, and can include high mood and racing thoughts (mania), depression, severe confusion, losing inhibitions, paranoia, hallucinations and delusions.

In contrast, about half of women have the maternity blues after birth, which is characterized by symptoms of mild mood swings, anxiety, and irritability that start about 3 to 4 days after delivery and last about a week; postpartum depression is also different — it is experienced by 10 to 15% of women after birth and is similar to major depressive disorder.

Brief reactive psychosis, referred to in the DSM IV-TR as "brief psychotic disorder with marked stressor(s)", is the psychiatric term for psychosis which can be triggered by an extremely stressful event in the life of an individual.

Typically such brief psychoses last from a day to a month only, with the delusions, speech disorders and hallucinations eventually yielding to a return to normal functioning.

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.

Postpartum psychosis is a psychiatric emergency related to care of women after they give birth. It is different from postpartum depression and from maternity blues.

The condition is not recognized in the DSM-5 nor in the ICD-10 but it is widely used clinically.

It may be a form of bipolar disorder.

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.

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 exact incidence and prevalence of brief psychotic disorder is not known, but it is generally considered uncommon. Internationally, it occurs twice as often in women than men, and even more often in women in the United States. It typically occurs in the late 30s and early 40s. The exact cause of brief psychotic disorder is not known. One theory suggests a genetic link, because the disorder is more common in people who have family members with mood disorders, such as depression or bipolar disorder. Another theory suggests that the disorder is caused by poor coping skills, as a defense against or escape from a particularly frightening or stressful situation. These factors may create a vulnerability to develop brief psychotic disorder. In most cases, the disorder is triggered by a major stress or traumatic event. Childbirth may trigger the disorder in some women. Approximately 1 in 10,000 women experience brief psychotic disorder shortly after childbirth. There are general medical causes of brief psychosis that should also be considered when being evaluated. Post-natal depression, HIV and AIDS, malaria, syphilis, Alzheimer's disease, Parkinson's disease, hypoglycaemia (an abnormally low level of glucose in the blood), lupus, multiple sclerosis, brain tumor and PANS.

Menstrual psychosis is a debated form of psychosis with a brief, sudden onset related to the menstrual cycle. The symptoms associated to it are dramatic and include delirium, mania or mutism. Most psychiatrists do not recognise the condition. Only 80 established cases are reported in medical literature and most of them were described by 19th Century physicians. It is thought to be linked with postpartum psychosis. This journal has been published looking at the 'evidence' for menstrual psychosis'.

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.

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.

Psychosis manifests as disorientation, visual hallucinations and/or haptic hallucinations. It is a state in which a person's mental capacity to recognize reality, communicate, and relate to others is impaired, thus interfering with the capacity to deal with life demands. While there are many types of psychosis, substance-induced psychosis can be pinpointed to specific chemicals.