Psychosis is first and foremost a diagnosis of exclusion. So a new-onset episode of psychosis "cannot" be considered a symptom of a psychiatric disorder until other relevant and known causes of psychosis are properly excluded, or ruled out. Many clinicians improperly perform, or entirely miss this step, introducing avoidable diagnostic error and misdiagnosis.

An initial assessment includes a comprehensive history and physical examination by a physician, psychiatrist, psychiatric nurse practitioner or psychiatric physician assistant. Biological tests should be performed to exclude psychosis associated with or caused by substance use, medication, toxins, surgical complications, or other medical illnesses.

Delirium should be ruled out, which can be distinguished by visual hallucinations, acute onset and fluctuating level of consciousness, indicating other underlying factors, including medical illnesses. Excluding medical illnesses associated with psychosis is performed by using blood tests to measure:

- Thyroid-stimulating hormone to exclude hypo- or hyperthyroidism,

- Basic electrolytes and serum calcium to rule out a metabolic disturbance,

- Full blood count including ESR to rule out a systemic infection or chronic disease, and

- Serology to exclude syphilis or HIV infection.

Other investigations include:

- EEG to exclude epilepsy, and an

- MRI or CT scan of the head to exclude brain lesions.

Because psychosis may be precipitated or exacerbated by common classes of medications, medication-induced psychosis should be ruled out, particularly for first-episode psychosis. Both substance- and medication-induced psychosis can be excluded to a high level of certainty, using a

- Urinalysis and a

- Full serum toxicology screening.

Because some dietary supplements may also induce psychosis or mania, but cannot be ruled out with laboratory tests, a psychotic individual's family, partner, or friends should be asked whether the patient is currently taking any dietary supplements.

Common mistakes made when diagnosing people who are psychotic include:

- Not properly excluding delirium,

- Not appreciating medical abnormalities (e.g., vital signs),

- Not obtaining a medical history and family history,

- Indiscriminate screening without an organizing framework,

- Missing a toxic psychosis by not screening for substances "and" medications

- Not asking family or others about dietary supplements,

- Premature diagnostic closure, and

- Not revisiting or questioning the initial diagnostic impression of primary psychiatric disorder.

Only after relevant and known causes of psychosis are excluded, a mental health clinician may make a psychiatric differential diagnosis using a person's family history, incorporating information from the person with psychosis, and information from family, friends, or significant others.

Types of psychosis in psychiatric disorders may be established by formal rating scales. The Brief Psychiatric Rating Scale (BPRS) assesses the level of 18 symptom constructs of psychosis such as hostility, suspicion, hallucination, and grandiosity. It is based on the clinician's interview with the patient and observations of the patient's behavior over the previous 2–3 days. The patient's family can also answer questions on the behavior report. During the initial assessment and the follow-up, both positive and negative symptoms of psychosis can be assessed using the 30 item Positive and Negative Symptom Scale (PANSS).

The evidence for the effectiveness of early interventions to prevent psychosis appeared inconclusive. Whilst early intervention in those with a psychotic episode might improve short term outcomes, little benefit was seen from these measures after five years. However, there is evidence that cognitive behavioral therapy (CBT) may reduce the risk of becoming psychotic in those at high risk, and in 2014 the UK National Institute for Health and Care Excellence (NICE) recommended preventive CBT for people at risk of psychosis.

Fink and Taylor developed a catatonia rating scale to identify the syndrome. A diagnosis is verified by a benzodiazepine or barbiturate test. The diagnosis is validated by the quick response to either benzodiazepines or electroconvulsive therapy (ECT). While proven useful in the past, barbiturates are no longer commonly used in psychiatry; thus the option of either benzodiazepines or ECT.

There is limited evidence that caffeine, in high doses or when chronically abused, may induce psychosis in normal individuals and worsen pre-existing psychosis in those diagnosed with schizophrenia.

According to the DSM-5, "Catatonia Associated with Another Mental Disorder (Catatonia Specifier)" (code 293.89 [F06.1]) is diagnosed if the clinical picture is dominated by at least three of the following:

- stupor (i.e., no psychomotor activity; not actively relating to environment)

- catalepsy (i.e., passive induction of a posture held against gravity)

- waxy flexibility (i.e., allow positioning by examiner and maintain position)

- mutism (i.e., no, or very little, verbal response [exclude if known aphasia])

- negativism (i.e., opposition or no response to instructions or external stimuli)

- posturing (i.e., spontaneous and active maintenance of a posture against gravity)

- mannerisms (i.e., odd, circumstantial caricature of normal actions)

- stereotypy (i.e., repetitive, abnormally frequent, non-goal-directed movements)

- agitation, not influenced by external stimuli

- grimacing (i.e. making a grimace like children)

- echolalia (i.e., mimicking another's speech)

- echopraxia (i.e., mimicking another's movements)

Other disorders (used additional code 293.89 [F06.1] to indicate the presence of the comorbid catatonia):

- Catatonia associated with autism spectrum disorder.

- Catatonia associated with schizophrenia spectrum and other psychotic disorders.

- Catatonia associated with brief psychotic disorder

- Catatonia associated with schizophreniform disorder

- Catatonia associated with schizoaffective disorder

- Catatonia associated with substance-induced psychotic disorder

- Catatonia associated with bipolar and related disorders.

- Catatonia associated with major depressive disorder

- Catatonic disorder due to another medical condition.

If catatonic symptoms are present but they are don't form the catatonic syndrome, a medication-induced or substance-induced aetiology should first be considered.

Treatment consists of supportive care during the acute intoxication phase: maintaining hydration, body temperature, blood pressure, and heart rate at acceptable levels until the drug is sufficiently metabolized to allow vital signs to return to baseline. Typical and atypical antipsychotics have been shown to be helpful in the early stages of treatment. This is followed by abstinence from psychostimulants supported with counseling or medication designed to assist the individual preventing a relapse and the resumption of a psychotic state.

There are few treatments for many types of hallucinations. However, for those hallucinations caused by mental disease, a psychologist or psychiatrist should be alerted, and treatment will be based on the observations of those doctors. Antipsychotic and atypical antipsychotic medication may also be utilized to treat the illness if the symptoms are severe and cause significant distress. For other causes of hallucinations there is no factual evidence to support any one treatment is scientifically tested and proven. However, abstaining from hallucinogenic drugs, stimulant drugs, managing stress levels, living healthily, and getting plenty of sleep can help reduce the prevalence of hallucinations. In all cases of hallucinations, medical attention should be sought out and informed of one's specific symptoms.

Cyclothymia, a condition of continuous mood fluctuations, is characterized by oscillating experiences of hypomania and depression that fail to meet the diagnostic criteria for either manic or major depressive episodes. These periods are often interspersed with periods of relatively normal (euthymic) functioning.

When a patient presents with a history of at least one episode of both hypomania and major depression, each of which meet the diagnostic criteria, bipolar II disorder is diagnosed. In some cases, depressive episodes routinely occur during the fall or winter and hypomanic ones in the spring or summer. In such cases, one speaks of a "seasonal pattern".

If left untreated, and in those so predisposed, hypomania may transition into mania, which may be psychotic, in which case bipolar I disorder is the correct diagnosis.

Oneirophrenic patients are resistant to insulin and when injected with glucose, these patients take 30 to 50% longer to return to normal glycemia. The meaning of this finding is not known, but it has been hypothesized that it may be due to an insulin antagonist present in the blood during psychosis. However, There is currently no known treatment for oneiophrenia.

Specifically, hypomania is distinguished from mania by the absence of psychotic symptoms and grandiosity, and by its lesser degree of impact on functioning.

Hypomania is a feature of bipolar II disorder and cyclothymia, but can also occur in schizoaffective disorder. Hypomania is also a feature of bipolar I disorder; it arises in sequential procession as the mood disorder fluctuates between normal mood (euthymia) and mania. Some individuals with bipolar I disorder have hypomanic as well as manic episodes. Hypomania can also occur when moods progress downwards from a manic mood state to a normal mood. Hypomania is sometimes credited with increasing creativity and productive energy. Numerous people with bipolar disorder have credited hypomania with giving them an edge in their theater of work.

People who experience hyperthymia, or "chronic hypomania", encounter the same symptoms as hypomania but on a longer-term basis.

One study from as early as 1895 reported that approximately 10% of the population experiences hallucinations. A 1996-1999 survey of over 13,000 people reported a much higher figure, with almost 39% of people reporting hallucinatory experiences, 27% of which daytime hallucinations, mostly outside the context of illness or drug use. From this survey, olfactory (smell) and gustatory (taste) hallucinations seem the most common in the general population.

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 DSM-IV-TR, paranoia is diagnosed in the form of:

- paranoid personality disorder ()

- paranoid schizophrenia (a subtype of schizophrenia) ()

- the persecutory type of delusional disorder, which is also called "querulous paranoia" when the focus is to remedy some injustice by legal action. ()

According to clinical psychologist P. J. McKenna, "As a noun, paranoia denotes a disorder which has been argued in and out of existence, and whose clinical features, course, boundaries, and virtually every other aspect of which is controversial. Employed as an adjective, paranoid has become attached to a diverse set of presentations, from paranoid schizophrenia, through paranoid depression, to paranoid personality—not to mention a motley collection of paranoid 'psychoses', 'reactions', and 'states'—and this is to restrict discussion to functional disorders. Even when abbreviated down to the prefix para-, the term crops up causing trouble as the contentious but stubbornly persistent concept of paraphrenia".

At least 50% of the diagnosed cases of schizophrenia experience delusions of reference and delusions of persecution. Paranoia perceptions and behavior may be part of many mental illnesses, such as depression and dementia, but they are more prevalent in three mental disorders: paranoid schizophrenia, delusional disorder (persecutory type), and paranoid personality disorder.

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.

Substance-induced psychosis (commonly known as toxic psychosis) is a form of substance use disorder where psychosis can be attributed to substance use. It is a psychosis that results from the poisonous effects of chemicals or drugs, including those produced by the body itself. Various psychoactive substances have been implicated in causing or worsening psychosis in users.

In ICD-10, this disorder is called depersonalization-derealization syndrome F48.1. The diagnostic criteria are as follows:

The diagnosis should not be given in certain specified conditions, for instance when intoxicated by alcohol or drugs, or together with schizophrenia, mood disorders and anxiety disorders.

Diagnosis is based on the self-reported experiences of the person followed by a clinical assessment. Psychiatric assessment includes a psychiatric history and some form of mental status examination. Since some medical and psychiatric conditions mimic the symptoms of DPD, clinicians must differentiate between and rule out the following to establish a precise diagnosis: temporal lobe epilepsy, panic disorder, acute stress disorder, schizophrenia, migraine, drug use, brain tumour or lesion. No laboratory test for depersonalization-derealization disorder currently exists.

The diagnosis of depersonalization disorder can be made with the use of the following interviews and scales:

The Structured Clinical Interview for DSM-IV Dissociative Disorders (SCID-D) is widely used, especially in research settings. This interview takes about 30 minutes to 1.5 hours, depending on individual's experiences.

The Dissociative Experiences Scale (DES) is a simple, quick, self-administered questionnaire that has been widely used to measure dissociative symptoms. It has been used in hundreds of dissociative studies, and can detect depersonalization and derealization experiences.

The Dissociative Disorders Interview Schedule (DDIS) is a highly structured interview which makes DSM-IV diagnoses of somatization disorder, borderline personality disorder and major depressive disorder, as well as all the dissociative disorders. It inquires about positive symptoms of schizophrenia, secondary features of dissociative identity disorder, extrasensory experiences, substance abuse and other items relevant to the dissociative disorders. The DDIS can usually be administered in 30–45 minutes.

The Cambridge Depersonalization Scale (CDS) is a method for determining the severity of depersonalization disorder. It has been proven and accepted as a valid tool for the diagnosis of depersonalization disorder in a clinical setting. It is also used in a clinical setting to differentiate minor episodes of depersonalization from actual symptoms of the disorder. Due to the success of the CDS, a group of Japanese researchers underwent the effort to translate the CDS into the J-CDS or the Japanese Cambridge Depersonalization Scale. Through clinical trials the Japanese research team successfully tested their scale and determined its accuracy. One limitation is that the scale does not allow for the differentiation between past and present episodes of depersonalization. It should also be noted that it may be difficult for the individual to describe the duration of a depersonalization episode, and thus the scale may lack accuracy. The project was conducted in the hope that it would stimulate further scientific investigations into depersonalization disorder.

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.

According to a substantial amount of epidemiology studies conducted, women are twice as likely to develop certain mood disorders, such as major depression. Although there is an equal number of men and women diagnosed with bipolar II disorder, women have a slightly higher frequency of the disorder.

In 2011, mood disorders were the most common reason for hospitalization among children aged 1–17 years in the United States, with approximately 112,000 stays. Mood disorders were top principal diagnosis for Medicaid super-utilizers in the United States in 2012. Further, a study of 18 States found that mood disorders accounted for the highest number of hospital readmissions among Medicaid patients and the uninsured, with 41,600 Medicaid patients and 12,200 uninsured patients being readmitted within 30 days of their index stay—a readmission rate of 19.8 per 100 admissions and 12.7 per 100 admissions, respectively. In 2012, mood and other behavioral health disorders were the most common diagnoses for Medicaid-covered and uninsured hospital stays in the United States (6.1% of Medicaid stays and 5.2% of uninsured stays).

A study conducted in 1988 to 1994 amongst young American adults involved a selection of demographic and health characteristics. A population-based sample of 8,602 men and women ages 17–39 years participated. Lifetime prevalence were estimated based on six mood measures:

1. major depressive episode (MDE) 8.6%,

2. major depressive disorder with severity (MDE-s) 7.7%,

3. dysthymia 6.2%,

4. MDE-s with dysthymia 3.4%,

5. any bipolar disorder 1.6%, and

6. any mood disorder 11.5%.

A 2012 paper suggested that, when compared with experiences today, psychiatric conditions associated with psychotic spectrum symptoms may be possible explanations for some revelatory driven experiences and activities such as those of Abraham, Moses, Jesus, and Saint Paul. However, the paper admits that the study was not aimed to deny supernatural elements, nor was it conclusive on whether their experiences were delusional in part or not at all.

Examples from a 295-subject study in Lithuania showed that the most common religious delusions were being a saint (in women) and being God (in men).

In one study of 193 people who had previously been admitted to hospital and subsequently diagnosed with schizophrenia, 24% were found to have religious delusions.

A 1999 study identified that religious delusions were often present or expressed in persons with forensic committal to a psychiatric unit.

The attribution model has been well talked about regarding paranoid or delusional individuals. The idea is that they like to assign issues to external events. A motivation behind this characteristic may involve the need for that person to develop a better self-image and maintain self-confidence. There have been debates about whether or not paranoid individuals are more likely to have a low or high self-perception, and results have been generated for both of these hypotheses. Researchers have made a distinction between positive self-esteem and negative self-esteem revealing that paranoid delusional individuals have more of a negative self-evaluation.

The DSM-5, released in May 2013, separates the mood disorder chapter from the DSM-TR-IV into two sections: Depressive and Related Disorders and Bipolar and Related Disorders. Bipolar Disorders falls in between Depressive Disorders and Schizophrenia Spectrum and Related Disorders “in recognition of their place as a bridge between the two diagnostic classes in terms of symptomatology, family history and genetics” (Ref. 1, p 123). Bipolar Disorders underwent a few changes in the DSM-5, most notably the addition of more specific symptomology related to hypomanic and mixed manic states. Depressive Disorders underwent the most changes, the addition of three new disorders: disruptive mood dysregulation disorder, persistent depressive disorder (previously dysthymia), and premenstrual dysphoric disorder (previously in Appendix B, the section for disorders needing further research). Disruptive mood dysregulation disorder is meant as a diagnosis for children and adolescents who would normally be diagnosed with bipolar disorder as a way to limit the bipolar diagnosis in this age cohort. Major depressive disorder (MDD) also underwent a notable change, in that the bereavement clause has been removed. Those previously exempt from a diagnosis of MDD due to bereavement are now candidates for the MDD diagnosis.

Tardive dysphrenia is characterized by a worsening of psychiatric symptoms that can be directly traced to the administration of antipsychotic medication.

Six symptoms are considered when diagnosing tardive dysphrenia:

A) The patient shows:

B) The symptoms are present for a full four weeks (full two weeks if successfully treated by immediate reinstitution or augmentation with a more potent drug and/or the rising of the previous drug) and contain any of these patterns:

C) Criteria A & B signs and symptoms emerge progressively with the administration of an oral antipsychotic drug or during the four-weeks period that follows its withdrawal (8 weeks for dépôt formulations).

D) There has been any exposure to a typical and/or atypical antipsychotic drug for at least three full months (full 12 weeks), or 1 full month (full 4 weeks) if the patient is sixty years old or older.

E) The clinical signs and symptoms cannot be attributed to another psychiatric condition, neurological condition, somatic illness, or severe stress. Also, exposure to other psychosis-inducing medicines must be excluded.

F) The signs and symptoms could not be better explained by an eventual previous psychiatric/neurological condition unfavorable natural evolution (i.e., Primary Refractory or poor prognosis Schizophrenia; severe Acute Mania; Dementia with Psychotic Symptoms) or by Neuroleptic Dysphoria.

For those whose sleepwalking episodes turn to be hazardous, a door alarm may offer a measure of protection. There are various kinds of door alarms that can attach to a bedroom door and when the door is opened, the alarm sounds off. The intention is that the sound will fully awaken the person and interrupt the sleepwalking episode, or if the sleepwalker lives with others, the sound will prompt them to check on the person.

Sleepwalkers should aim to have their bedrooms on the first floor of a home, apartment, dorm, hotel, etc.

Also, sleepwalkers should not have easily accessible weapons (loaded guns, knives) in the bedroom or any room of the house for that matter. If there are weapons, they should be locked away with keys secluded from the sleepwalker.