Dissociative disorders (DD) are conditions that involve disruptions or breakdowns of memory, awareness, identity, or perception. People with dissociative disorders use dissociation, as a defence mechanism, pathologically and involuntarily. Dissociative disorders are sometimes triggered by psychological trauma, but may be preceded only by stress, psychoactive substances, or no identifiable trigger at all.

The dissociative disorders listed in the American Psychiatric Association's DSM-5 are as follows:

- Dissociative identity disorder (formerly multiple personality disorder): the alternation of two or more distinct personality states with impaired recall among personality states. In extreme cases, the host personality is unaware of the other, alternating personalities; however, the alternate personalities can be aware of all the existing personalities. This category now includes the old derealization disorder category.

- Dissociative amnesia (formerly psychogenic amnesia): the temporary loss of recall memory, specifically episodic memory, due to a traumatic or stressful event. It is considered the most common dissociative disorder amongst those documented. This disorder can occur abruptly or gradually and may last minutes to years depending on the severity of the trauma and the patient.

- Dissociative fugue (formerly psychogenic fugue) is now subsumed under the dissociative amnesia category. It is described as reversible amnesia for personal identity, usually involving unplanned travel or wandering, sometimes accompanied by the establishment of a new identity. This state is typically associated with stressful life circumstances and can be short or lengthy.

- Depersonalization disorder: periods of detachment from self or surrounding which may be experienced as "unreal" (lacking in control of or "outside" self) while retaining awareness that this is only a feeling and not a reality.

- The old category of dissociative disorder not otherwise specified is now split into two: Other specified dissociative disorder, and unspecified dissociative disorder. These categories are used for forms of pathological dissociation that do not fully meet the criteria of the other specified dissociative disorders, or if the correct category has not been determined.

Both dissociative amnesia and dissociative fugue usually emerge in adulthood and rarely occur after the age of 50. The ICD-10 classifies conversion disorder as a dissociative disorder while the DSM-IV classifies it as a somatoform 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.

Dissociative identity disorder (multiple personality disorder)

Cause: People with dissociative identity disorder usually have close relatives who have also had similar experiences.

Treatment: Long-term psychotherapy that helps the patient merge his/her multiple personalities into one personality. “The trauma of the past has to be explored and resolved with proper emotional expression. Hospitalization may be required if behavior becomes bizarre or destructive”. Dissociative identity disorder has a tendency to recur over a period of several years, and may become less of a problem after mid-life.

Dissociative amnesia

Cause: A way to cope with trauma.

Treatment: Psychotherapy (e.g. talk therapy) counseling or psychosocial therapy which involves talking about your disorder and related issues with a mental health provider. Psychotherapy often involves hypnosis (help you remember and work through the trauma); creative art therapy (using creative process to help a person who cannot express his or her thoughts); cognitive therapy (talk therapy to identify unhealthy and negative beliefs/behaviors); and medications (antidepressants, anti-anxiety medications or tranquilizers). These medications help control the mental health symptoms associated with the disorders, but there are no medications that specifically treat dissociative disorders. However, the medication Pentothal can sometimes help to restore the memories. The length of an event of dissociative amnesia may be a few minutes or several years. If an episode is associated with a traumatic event, the amnesia may clear up when the person is removed from the traumatic situation.

Dissociative fugue

Cause: A stressful event that happens in adulthood.

Treatment: Hypnosis is often used to help patient recall true identity and remember events of the past. Psychotherapy is helpful for the person who has traumatic, past events to resolve. Once dissociative fugue is discovered and treated, many people recover quickly. The problem may never happen again.

Depersonalization disorder

Cause: Dissociative disorders usually develop as a way to cope with trauma. The disorders most often form in children subjected to chronic physical, sexual or emotional abuse or, less frequently, a home environment that is otherwise frightening or highly unpredictable; however, this disorder can also acutely form due to severe traumas such as war or the death of a loved one.

Treatment: Same treatment as dissociative amnesia, and same drugs. An episode of depersonalization disorder can be as brief as a few seconds or continue for several years.

Conversion disorder is now contained under the umbrella term functional neurological symptom disorder. In cases of conversion disorder, there is a psychological stressor.

The diagnostic criteria for functional neurological symptom disorder, as set out in DSM-V, are:

Specify type of symptom or deficit as:

- With weakness or paralysis

- With abnormal movement (e.g. tremor, dystonic movement, myoclonus, gait disorder)

- With swallowing symptoms

- With speech symptoms (e.g. dysphonia, slurred speech)

- With attacks or seizures

- With amnesia or memory loss

- With special sensory symptom (e.g. visual, olfactory, or hearing disturbance)

- With mixed symptoms.

Specify if:

- Acute episode: symptoms present for less than six months

- Persistent: symptoms present for six months or more.

Specify if:

- Psychological stressor (conversion disorder)

- No psychological stressor (functional neurological symptom disorder)

Conversion disorder begins with some stressor, trauma, or psychological distress. Usually the physical symptoms of the syndrome affect the senses or movement. Common symptoms include blindness, partial or total paralysis, inability to speak, deafness, numbness, difficulty swallowing, incontinence, balance problems, seizures, tremors, and difficulty walking. These symptoms are attributed to conversion disorder when a medical explanation for the afflictions cannot be found. Symptoms of conversion disorder usually occur suddenly. Conversion disorder is typically seen in individuals aged 10 to 35, and affects between 0.011% and 0.5% of the general population.

Conversion disorder can present with motor or sensory symptoms including any of the following:

Motor symptoms or deficits:

- Impaired coordination or balance

- Weakness/paralysis of a limb or the entire body (hysterical paralysis or motor conversion disorders)

- Impairment or loss of speech (hysterical aphonia)

- Difficulty swallowing (dysphagia) or a sensation of a lump in the throat

- Urinary retention

- Psychogenic non-epileptic seizures or convulsions

- Persistent dystonia

- Tremor, myoclonus or other movement disorders

- Gait problems (astasia-abasia)

- Loss of consciousness (fainting)

Sensory symptoms or deficits:

- Impaired vision (hysterical blindness), double vision

- Impaired hearing (deafness)

- Loss or disturbance of touch or pain sensation

Conversion symptoms typically do not conform to known anatomical pathways and physiological mechanisms. It has sometimes been stated that the presenting symptoms tend to reflect the patient's own understanding of anatomy and that the less medical knowledge a person has, the more implausible are the presenting symptoms. However, no systematic studies have yet been performed to substantiate this statement.

Factitious disorder should be distinguished from somatic symptom disorder (formerly called somatization disorder), in which the patient is truly experiencing the symptoms and has no intention to deceive.

In conversion disorder (previously called hysteria), a neurological deficit appears with no organic cause. The patient, again, is truly experiencing the symptoms and signs and has no intention to deceive.

The differential also includes body dysmorphic disorder and pain disorder.

Ganser syndrome was once considered a separate factitious disorder. It is a disorder of extreme stress or an organic condition. The patient suffers from approximation or giving absurd answers to simple questions. The syndrome is sometimes diagnosed as merely malingering—however, it is more often defined as a factitious disorder. This has been seen in prisoners following solitary confinement, and the symptoms are consistent in different prisons, though the patients do not know one another.

Symptoms include a clouding of consciousness, somatic conversion symptoms, confusion, stress, loss of personal identity, echolalia, and echopraxia. Individuals also give approximate answers to simple questions such as, "How many legs on a cat?" "Three"; "What's the day after Wednesday?" "Friday"; and so on. The disorder is extraordinarily rare with fewer than 100 recorded cases. 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, though it stretches from ages 15–62 years old.

Somatic symptom disorders are a group of disorders, all of which fit the definition of physical symptoms similar to those observed in physical disease or injury for which there is no identifiable physical cause. As such, they are a diagnosis of exclusion. Somatic symptoms may be generalized in four major medical categories: neurological, cardiac, pain, and gastrointestinal somatic symptoms.

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.

A somatic symptom disorder, formerly known as a somatoform disorder, is any mental disorder which manifests as physical symptoms that suggest illness or injury, but which cannot be explained fully by a general medical condition or by the direct effect of a substance, and are not attributable to another mental disorder (e.g., panic disorder). Somatic symptom disorders, as a group, are included in a number of diagnostic schemes of mental illness, including the "Diagnostic and Statistical Manual of Mental Disorders". (Before DSM-5 this disorder was split into "somatization disorder" and "undifferentiated somatoform disorder".)

In people who have been diagnosed with a somatic symptom disorder, medical test results are either normal or do not explain the person's symptoms, and history and physical examination do not indicate the presence of a known medical condition that could cause them, though it is important to note that the DSM-5 cautions that this alone is not sufficient for diagnosis. The patient must also be excessively worried about their symptoms, and this worry must be judged to be out of proportion to the severity of the physical complaints themselves. A diagnosis of somatic symptom disorder requires that the subject have recurring somatic complaints for at least six months.

Symptoms are sometimes similar to those of other illnesses and may last for years. Usually, the symptoms begin appearing during adolescence, and patients are diagnosed before the age of 30 years. Symptoms may occur across cultures and gender. Other common symptoms include anxiety and depression. However, since anxiety and depression are also very common in persons with confirmed medical illnesses, it remains possible that such symptoms are a consequence of the physical impairment, rather than a cause. Somatic symptom disorders are not the result of conscious malingering (fabricating or exaggerating symptoms for secondary motives) or factitious disorders (deliberately producing, feigning, or exaggerating symptoms). Somatic symptom disorder is difficult to diagnose and treat. Some advocates of the diagnosis believe this is because proper diagnosis and treatment requires psychiatrists to work with neurologists on patients with this disorder.

The original description by Sigbert Josef Maria Ganser in 1898 pointed out their hysterical twilight state. They may also describe hallucinations which are usually more than those in schizophrenia. They may also have disorders of sensation similar to those in conversion disorder. They may be inattentive or drowsy.

Some workers believe there is a genuine psychosis underlying this, others believe it is a dissociative disorder, while still others believe it is the result of malingering. Over the years, opinions have seemed to move from the last view more towards the first.

Ganser syndrome is currently classified under dissociative disorders, to which it moved in the DSM IV from the factitious disorders.

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.

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.

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.

There are a great number of symptoms experienced by those with a functional neurological disorder. It is important to note that the symptoms experienced by those with an FND are very real , and should not be confused with malingering, factitious disorders, or Munchausen syndrome. At the same time, the origin of symptoms is complex since it can be associated with physical injury, severe psychological trauma (conversion disorder), and idiopathic neurological dysfunction. The core symptoms are those of motor or sensory function or episodes of altered awareness

- Limb weakness or paralysis

- Blackouts (also called dissociative or non-epileptic seizures/attacks) – these may look like epileptic seizures or faints

- Movement disorders including tremors, dystonia (spasms), myoclonus (jerky movements)

- Visual symptoms including loss of vision or double vision

- Speech symptoms including dysphonia (whispering speech), slurred or stuttering speech

- Sensory disturbance including hemisensory syndrome (altered sensation down one side of the body)

Functional neurological disorders are a common problem, and are the second most common reason for a neurological outpatient visit after headache/migraine. Dissociative (non-epileptic) seizures account for about 1 in 7 referrals to neurologists after an initial seizure, and functional weakness has a similar prevalence to multiple sclerosis.

Neurological disorders can be categorized according to the primary location affected, the primary type of dysfunction involved, or the primary type of cause. The broadest division is between central nervous system disorders and peripheral nervous system disorders. The Merck Manual lists brain, spinal cord and nerve disorders in the following overlapping categories:

- Brain:

- Brain damage according to cerebral lobe "(see also 'lower' brain areas such as basal ganglia, cerebellum, brainstem)":

- Frontal lobe damage

- Parietal lobe damage

- Temporal lobe damage

- Occipital lobe damage

- Brain dysfunction according to type:

- Aphasia (language)

- Dysgraphia (writing)

- Dysarthria (speech)

- Apraxia (patterns or sequences of movements)

- Agnosia (identifying things or people)

- Amnesia (memory)

- Spinal cord disorders (see spinal pathology, injury, inflammation)

- Peripheral neuropathy and other Peripheral nervous system disorders

- Cranial nerve disorder such as Trigeminal neuralgia

- Autonomic nervous system disorders such as dysautonomia, Multiple System Atrophy

- Seizure disorders such as epilepsy

- Movement disorders of the central and peripheral nervous system such as Parkinson's disease, Essential tremor, Amyotrophic lateral sclerosis, Tourette's Syndrome, Multiple Sclerosis and various types of Peripheral Neuropathy

- Sleep disorders such as Narcolepsy

- Migraines and other types of Headache such as Cluster Headache and Tension Headache

- Lower back and neck pain (see Back pain)

- Central neuropathy (see Neuropathic pain)

- Neuropsychiatric illnesses (diseases and/or disorders with psychiatric features associated with known nervous system injury, underdevelopment, biochemical, anatomical, or electrical malfunction, and/or disease pathology e.g. Attention deficit hyperactivity disorder, Autism, Tourette's syndrome and some cases of obsessive compulsive disorder as well as the neurobehavioral associated symptoms of degeneratives of the nervous system such as Parkinson's disease, essential tremor, Huntington's disease, Alzheimer's disease, multiple sclerosis and organic psychosis.)

Many of the diseases and disorders listed above have neurosurgical treatments available (e.g. Tourette's Syndrome, Parkinson's disease, Essential tremor and Obsessive compulsive disorder).

- Delirium and dementia such as Alzheimer's disease

- Dizziness and vertigo

- Stupor and coma

- Head injury

- Stroke (CVA, cerebrovascular attack)

- Tumors of the nervous system (e.g. cancer)

- Multiple sclerosis and other demyelinating diseases

- Infections of the brain or spinal cord (including meningitis)

- Prion diseases (a type of infectious agent)

- Complex regional pain syndrome (a chronic pain condition)

Neurological disorders in non-human animals are treated by veterinarians.

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.

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.

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.

Common symptoms of pain disorder are: negative or distorted cognition, such as feelings of despair or hopelessness; inactivity and passivity, in some cases disability; increased pain, sometimes requiring clinical treatment; sleep disturbance and fatigue; disruption of social relationships; depression and/or anxiety. Acute conditions last less than six months while chronic pain disorder lasts six or more months.

There is no neurological or physiological basis for the pain. Pain is reported as more distressing than it should be if there was a physical explanation. People who suffer from this disorder may begin to abuse medication.

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.

Qualities of MPI outbreaks often include:

- symptoms that have no plausible organic basis;

- symptoms that are transient and benign;

- symptoms with rapid onset and recovery;

- occurrence in a segregated group;

- the presence of extraordinary anxiety;

- symptoms that are spread via sight, sound or oral communication;

- a spread that moves down the age scale, beginning with older or higher-status people;

- a preponderance of female participants

Also, the illness may recur after the initial outbreak.

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."

Ego-dystonic sexual orientation is an ego-dystonic mental disorder characterized by having a sexual orientation or an attraction that is at odds with one's idealized self-image, causing anxiety and a desire to change one's orientation or become more comfortable with one's sexual orientation. It describes not innate sexual orientation itself, but a conflict between the sexual orientation one wishes to have and the sexual orientation one actually possesses.