The lifetime prevalence of dissociative disorders varies from 10% in the general population to 46% in psychiatric inpatients. Diagnosis can be made with the help of structured interviews such as the Dissociative Disorders Interview Schedule (DDIS) and the Structured Clinical Interview for DSM-IV Dissociative Disorders (SCID-D), or with the Dissociative Experiences Scale (DES) which is a self-assessment questionnaire. Some diagnostic tests have also been adapted and/or developed for use with children and adolescents such as the Children's Version of the Response Evaluation Measure (REM-Y-71), Child Interview for Subjective Dissociative Experiences, Child Dissociative Checklist (CDC), Child Behavior Checklist (CBCL) Dissociation Subscale, and the Trauma Symptom Checklist for Children Dissociation Subscale.

There are problems with classification, diagnosis and therapeutic strategies of dissociative and conversion disorders which can be understood by the historic context of hysteria. Even current systems used to diagnose DD such as the DSM-IV and ICD-10 differ in the way the classification is determined. In most cases mental health professionals are still hesitant to diagnose patients with Dissociative Disorder, because before they are considered to be diagnosed with Dissociative Disorder these patients have more than likely been diagnosed with major depression, anxiety disorder, and most often post-traumatic disorder.

An important concern in the diagnosis of dissociative disorders is the possibility that the patient may be feigning symptoms in order to escape negative consequences. Young criminal offenders report much higher levels of dissociative disorders, such as amnesia. In one study it was found that 1% of young offenders reported complete amnesia for a violent crime, while 19% claimed partial amnesia. There have also been incidences in which people with dissociative identity disorder provide conflicting testimonies in court, depending on the personality that is present.

Dissociative disorders (DD) are widely believed to have roots in traumatic childhood experience (abuse or loss), but symptomology often goes unrecognized or is misdiagnosed in children and adolescents. There are several reasons why recognizing symptoms of dissociation in children is challenging: it may be difficult for children to describe their internal experiences; caregivers may miss signals or attempt to conceal their own abusive or neglectful behaviors; symptoms can be subtle or fleeting; disturbances of memory, mood, or concentration associated with dissociation may be misinterpreted as symptoms of other disorders.

In addition to developing diagnostic tests for children and adolescents (see above), a number of approaches have been developed to improve recognition and understanding of dissociation in children. Recent research has focused on clarifying the neurological basis of symptoms associated with dissociation by studying neurochemical, functional and structural brain abnormalities that can result from childhood trauma. Others in the field have argued that recognizing disorganized attachment (DA) in children can help alert clinicians to the possibility of dissociative disorders.

Clinicians and researchers also stress the importance of using a developmental model to understand both symptoms and the future course of DDs. In other words, symptoms of dissociation may manifest differently at different stages of child and adolescent development and individuals may be more or less susceptible to developing dissociative symptoms at different ages. Further research into the manifestation of dissociative symptoms and vulnerability throughout development is needed. Related to this developmental approach, more research is required to establish whether a young patient’s recovery will remain stable over time.

Empirical studies have found that the prognosis for conversion disorder varies widely, with some cases resolving in weeks, and others enduring for years or decades. There is also evidence that there is no cure for Conversion Disorder, and that although patients may go into remission, they can relapse at any point. Furthermore, many patients who are 'cured' continue to have some degree of symptoms indefinitely.

Information on the frequency of conversion disorder in the West is limited, in part due to the complexities of the diagnostic process. In neurology clinics, the reported prevalence of unexplained symptoms among new patients is very high (between 30 and 60%). However, diagnosis of conversion typically requires an additional psychiatric evaluation, and since few patients will see a psychiatrist it is unclear what proportion of the unexplained symptoms are actually due to conversion. Large scale psychiatric registers in the US and Iceland found incidence rates of 22 and 11 newly diagnosed cases per 100,000 person-years, respectively. Some estimates claim that in the general population, between 0.011% and 0.5% of the population have conversion disorder.

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

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

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

There are many possible causes for this disorder. One such possibility is an underlying personality disorder. Individuals with FD may be trying to repeat a satisfying childhood relationship with a doctor. Perhaps also an individual has a desire to deceive or test authority figures. The underlying desire to resume the role of a patient and be cared for can also be considered an underlying personality disorder. Abuse, neglect, or abandonment during childhood are also probable causes.

These individuals may be trying to reenact unresolved issues with their parents. A history of frequent illnesses may also contribute to the development of this disorder. In some cases, individuals afflicted with FD are accustomed to actually being sick, and thus return to their previous state to recapture what they once considered the 'norm.' Another cause is a history of close contact with someone (a friend or family member) who had a severe or chronic condition. The patients found themselves subconsciously envious of the attention said relation received, and felt that they themselves faded into the background. Thus medical attention makes them feel glamorous and special.

Some individuals experience only a few outbreaks of the disorder. However, in most cases, factitious disorder is a chronic and long-term condition that is difficult to treat. There are relatively few positive outcomes for this disorder; in fact, treatment provided a lower percentage of positive outcomes than did treatment of individuals with obvious psychotic symptoms such as people with schizophrenia. In addition, many individuals with factitious disorder do not present for treatment, often insisting their symptoms are genuine. Some degree of recovery, however, is possible. The passage of time seems to help the disorder greatly. There are many possible explanations for this occurrence, although none are currently considered definitive. It may be that an FD individual has mastered the art of feigning sickness over so many years of practice that the disorder can no longer be discerned. Another hypothesis is that many times an FD individual is placed in a home, or experiences health issues that are not self-induced or feigned. In this way, the problem with obtaining the 'patient' status is resolved because symptoms arise without any effort on the part of the individual.

The disorder is extraordinarily rare. While individuals of all backgrounds have been reported with the disorder, there is a higher inclination towards males (75% or more). The average age of those with Ganser syndrome is 32 and it stretches from ages 15 to 62 years old. It has been reported in children.

The disorder is apparently most common in men and prisoners, although prevalence data and familial patterns are not established.

In the opinion of Allen Frances, chair of the DSM-IV task force, the DSM-5's somatic symptom disorder brings with it a risk of mislabeling a sizable proportion of the population as mentally ill. “Millions of people could be mislabeled, with the burden falling disproportionately on women, because they are more likely to be casually dismissed as ‘catastrophizers’ when presenting with physical symptoms.”

Psychotherapy, more specifically, cognitive behavioral therapy (CBT), is the most widely used form of treatment for Somatic symptom disorder. In 2016, a randomized 12-week study suggested steady and significant improvement in health anxiety measures with cognitive behavioral therapy compared to the control group.

CBT can help in some of the following ways:

- Learn to reduce stress

- Learn to cope with physical symptoms

- Learn to deal with depression and other psychological issues

- Improve quality of life

- Reduce preoccupation with symptom

Moreover, brief psychodynamic interpersonal psychotherapy (PIT) for patients with multisomatoform disorder has shown its long-term efficacy for improving the physical quality of life in patients with multiple, difficult-to-treat, medically unexplained symptoms.

Antidepressant medication has also been used to treat some of the symptoms of depression and anxiety that are common among people who have somatic symptom disorder. Medications will not cure somatic symptom disorder, but can help the treatment process when combined with CBT.

Zou huo ru mo (走火入魔) or "qigong deviation" (气功出偏), is a Chinese term traditionally used to indicate that something has gone wrong in spiritual or martial arts training, applied to describe a physiological or psychological disorder believed to result during or after qigong practice, believed by the qigong community to result from "improper practice" of qigong and other self-cultivation techniques, and highlighted in the social and political context of mass popularization of qigong in China.

Ganser syndrome is a rare dissociative disorder previously classified as a factitious disorder. It is characterized by nonsensical or wrong answers to questions or doing things incorrectly, other dissociative symptoms such as fugue, amnesia or conversion disorder, often with visual pseudohallucinations and a decreased state of consciousness. It is also sometimes called nonsense syndrome, balderdash syndrome, syndrome of approximate answers, hysterical pseudodementia or prison psychosis. This last name, prison psychosis, is sometimes used because the syndrome occurs most frequently in prison inmates, where it may be seen as an attempt to gain leniency from prison or court officials.

Ganser is an extremely rare variation of dissociative disorder. It is a reaction to extreme stress and the patient thereby suffers from approximation or giving absurd answers to simple questions. The syndrome can sometimes be diagnosed as merely malingering, but it is more often defined as dissociative disorder.

Symptoms include a clouding of consciousness, somatic conversion symptoms, confusion, stress, loss of personal identity, echolalia, and echopraxia. The psychological symptoms generally resemble the patient's sense of mental illness rather than any recognized category. Individuals also give approximate answers to simple questions. For example, "How many legs are on a cat?", to which the subject may respond 'Three'.

The syndrome may occur in persons with other mental disorders such as schizophrenia, depressive disorders, toxic states, paresis, alcohol use disorders and factitious disorders. EEG data does not suggest any specific organic cause.

Research is ongoing in many aspects of functional neurological disorders but large studies are needed to definitely answer key questions including:

What is the best treatment for patients with FND? Even disorders like multiple sclerosis and Parkinson's disease have no definite known cause. The importance of increased awareness in the medical world of what constitutes a positive diagnosis of FND and what the best treatments are may, in the short term, be where research is focused.

Functional neurological symptom disorder can mimic many other conditions. Some alternative diagnoses for FND include:

- Hemiplegic migraine

- Multiple sclerosis

- Motor neurone disease

- Parkinson's

- Autoimmune disorders

- Ehlers–Danlos syndrome

- Stroke

- Vitamin B12 deficiency or pernicious anaemia

- Myasthenia gravis

A pseudohallucination is an involuntary sensory experience vivid enough to be regarded as a hallucination, but recognised by the patient not to be the result of external stimuli. Unlike normal hallucinations, which occurs when one sees, hears, smells, tastes or feels something that is not there, with a compelling feeling or thought that it is real, pseudohallucinations are recognised by the person as unreal.

In other words, it is a hallucination that is recognized as a hallucination, as opposed to a "normal" hallucination which would be perceived as real. An example used in psychiatry is the hearing of voices which are "inside the head" according to the patient; in contrast, a hallucination would be indistinguishable to the patient from a real external stimulus, e.g. "people were talking about me".

The term is not widely used in the psychiatric and medical fields, as it is considered ambiguous; the term "nonpsychotic hallucination" is preferred. Pseudohallucinations, then, are more likely to happen with a hallucinogenic drug. But "the current understanding of pseudohallucinations is mostly based on the work of Karl Jaspers".

A further distinction is sometimes made between pseudohallucinations and "parahallucinations", the latter being a result of damage to the peripheral nervous system.

They are considered a feature of conversion disorder, somatization disorder, and dissociative disorders. Also, pseudohallucinations can occur in people with visual/hearing loss, with the typical such type being Charles Bonnet syndrome.

Symptoms are often identified as being in one of three categories:

1. panic, discomfort, and uncontrolled spontaneous movement;

2. sensory problems, such as visual or auditory hallucination; and

3. irrational beliefs.

Somatic symptoms can include sensations and pain in head, chest and back, abdomen, limbs, or whole body; whereas, mental and emotional symptoms can include neurasthenia, affective disorder, self-consciousness, hallucination, and paranoia.

Although the brain and spinal cord are surrounded by tough membranes, enclosed in the bones of the skull and spinal vertebrae, and chemically isolated by the blood–brain barrier, they are very susceptible if compromised. Nerves tend to lie deep under the skin but can still become exposed to damage. Individual neurons, and the neural networks and nerves into which they form, are susceptible to electrochemical and structural disruption. Neuroregeneration may occur in the peripheral nervous system and thus overcome or work around injuries to some extent, but it is thought to be rare in the brain and spinal cord.

The specific causes of neurological problems vary, but can include genetic disorders, congenital abnormalities or disorders, infections, lifestyle or environmental health problems including malnutrition, and brain injury, spinal cord injury or nerve injury. The problem may start in another body system that interacts with the nervous system. For example, cerebrovascular disorders involve brain injury due to problems with the blood vessels (cardiovascular system) supplying the brain; autoimmune disorders involve damage caused by the body's own immune system; lysosomal storage diseases such as Niemann-Pick disease can lead to neurological deterioration. The National Institutes of Health recommend considering the evaluation of an underlying celiac disease in people with unexplained neurological symptoms, particularly peripheral neuropathy or ataxia.

In a substantial minority of cases of neurological symptoms, no neural cause can be identified using current testing procedures, and such "idiopathic" conditions can invite different theories about what is occurring.

At least once a week, 10-30% of those under 18 years of age suffer from unexplainable headaches and abdominal pains in the United States, and the number is rising. People from collectivistic countries such as Japan, China, and Mexico are more likely to suffer from pain disorder than individualistic countries such as the US and Sweden.

Pseudodementia is a phenotype approximated by a wide variety of underlying disorders (1). Data indicate that some of the disorders that can convert to a pseudodementia-like presentation include depression (mood), schizophrenia, mania, dissociative disorders, Ganser syndrome, conversion reaction, and psychoactive drugs (2). Although the frequency distribution of disorders presenting as pseudodementia remains unclear, what is clear is that depressive pseudodementia, synonymously referred to as depressive dementia(3) or major depression with depressive dementia (4), represents a major subclass of the overarching category of pseudodementia (4).

It has long been observed that in the differential diagnosis between dementia and pseudodementia, depressive pseudodementia appears to be the single most difficult disorder to distinguish from nosologically established "organic" categories of dementia(5), especially degenerative dementia of the Alzheimer type (6).

Depressive Pseudodementia is a syndrome seen in older people in which they exhibit symptoms consistent with dementia but the cause is actually depression.

Older people with predominant cognitive symptoms such as loss of memory, and vagueness, as well as prominent slowing of movement and reduced or slowed speech, were sometimes misdiagnosed as having dementia when further investigation showed they were suffering from a major depressive episode. This was an important distinction as the former was untreatable and progressive and the latter treatable with antidepressant therapy or electroconvulsive therapy or both. In contrast to major depression, dementia is a progressive neurodegenerative syndrome involving a pervasive impairment of higher cortical functions resulting from widespread brain pathology.

A neurological disorder is any disorder of the nervous system. Structural, biochemical or electrical abnormalities in the brain, spinal cord or other nerves can result in a range of symptoms. Examples of symptoms include paralysis, muscle weakness, poor coordination, loss of sensation, seizures, confusion, pain and altered levels of consciousness. There are many recognized neurological disorders, some relatively common, but many rare. They may be assessed by neurological examination, and studied and treated within the specialities of neurology and clinical neuropsychology.

Interventions for neurological disorders include preventative measures, lifestyle changes, physiotherapy or other therapy, neurorehabilitation, pain management, medication, or operations performed by neurosurgeons. The World Health Organization estimated in 2006 that neurological disorders and their sequelae (direct consequences) affect as many as one billion people worldwide, and identified health inequalities and social stigma/discrimination as major factors contributing to the associated disability and suffering.

Ethnicities show differences in how they express their discomfort and on how acceptable shows of pain and its tolerance are.

Most obvious in adolescence, females suffer from this disorder more than males, and females reach out more.

More unexplainable pains occur as people get older. Typically, younger children complain of only one symptom, commonly abdominal pains or headaches. The older they get, the more varied the pain location as well as more locations and increasing frequency.

The hypothesis that those prone to extroversion or neuroticism, or those with low IQ scores, are more likely to be affected in an outbreak of hysterical epidemic has not been consistently supported by research. Bartholomew and Wesseley state that it “seems clear that there is no particular predisposition to mass sociogenic illness and it is a behavioural reaction that anyone can show in the right circumstances.”

Females are affected with mass psychogenic illness at greater rates than males. Adolescents and children are frequently affected in cases of MPI.

Timothy F. Jones, of the Tennessee Department of Health, recommends the following action be taken in the case of an outbreak:

- Attempt to separate persons with illness associated with the outbreak.

- Promptly perform physical examination and basic laboratory testing sufficient to exclude serious acute illness.

- Monitor and provide oxygen as necessary for hyperventilation.

- Minimize unnecessary exposure to medical procedures, emergency personnel, media or other potential anxiety-stimulating situations.

- Notify public health authorities of apparent outbreak.

- Openly communicate with physicians caring for other patients.

- Promptly communicate results of laboratory and environmental testing to patients.

- While maintaining confidentiality, explain that other people are experiencing similar symptoms and improving without complications.

- Remind patients that rumors and reports of "suspected causes" are not equivalent to confirmed results.

- Acknowledge that symptoms experienced by the patient are real.

- Explain potential contribution of anxiety to the patient's symptoms.

- Reassure patient that long-term sequelae from current illness are not expected.

- As appropriate, reassure patient that thorough clinical, epidemiologic and environmental investigations have identified no toxic cause for the outbreak or reason for further concern.

Some responses by authorities to MPI are not appropriate. Intense media coverage seems to exacerbate outbreaks. Once it is determined that the illness is psychogenic, it should not be given credence by authorities. For example, in the Singapore factory case study, calling in a medicine man to perform an exorcism seemed to perpetuate the outbreak.

The history of disturbance in pseudodementia is often short and abrupt onset, while dementia is more often insidious. Clinically, people with pseudodementia differ from those with true dementia when their memory is tested. They will often answer that they don't know the answer to a question, and their attention and concentration are often intact, and they may appear upset or distressed. Those with true dementia will often give wrong answers, have poor attention and concentration, and appear indifferent or unconcerned.

Investigations such as SPECT imaging of the brain show reduced blood flow in areas of the brain in people with Alzheimer's disease, compared with a more normal blood flow in those with pseudodementia.

Autassassinophilia is a paraphilia in which a person is sexually aroused by the risk of being killed. The fetish may overlap with some other fetishes that risk one's life, such as those involving drowning or choking. This does not necessarily mean the person must actually be in a life-threatening situation, for many are aroused from dreams and fantasies of such.

The term was introduced by John Money who also defined erotophonophilia as the "reciprocal condition" in which one is aroused by "stage-managing and carrying out the murder of an unsuspecting sexual partner". Money classified both these paraphilias as "of the sacrificial/expiatory type". These concepts, especially their imperfect reciprocity, were criticized by Lisa Downing who wrote that

"The autassassinophiliac, for Money, is more interested in his orgasm than in his death, resulting in a compulsion to 'stage manage the "possibility" rather than the "actuality" of his end at the hands of another person. The erotophonophiliac, on the other hand, is driven by the actualization of the other's death and – crucially – this other must be unaware of the would-be killer's intentions. These definitions, then, effectively preclude reciprocity and are constructed here in such a way as to prevent the possibility of consent. The sexologist, it seems, is incapable of imagining mutuality in this context. [...] The imagined pact is used here as an incentive to the would-be libertarian to support the suppression of paraphilia and the conversion of a death-related desire to a life-giving form."