Dissociative amnesia

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Dissociative amnesia is amnesia (memory loss) caused by trauma or stress, resulting in an inability to recall important personal information.

People have gaps in their memory, which may span a few minutes to decades.
After tests are done to rule out other possible causes, doctors diagnose the disorder based on symptoms.
Memory-retrieval techniques, including hypnosis and drug-facilitated interviews, are used to fill in the memory gaps.
Psychotherapy is needed to help people deal with the experiences that triggered the disorder.

(See also Overview of Dissociative Disorders and Memory Loss.)
Amnesia is the total or partial inability to recall recent experiences or ones from the distant past. When amnesia is caused by a psychologic rather than a physical disturbance, it is called dissociative amnesia.
In dissociative amnesia, the lost memory usually involves information that is normally part of routine conscious awareness or autobiographic memory:

Who one is
Where one went
To whom one spoke
What one did, said, thought, and felt

Often, the lost memory is information about traumatic or stressful events, such as childhood abuse. Sometimes the information, though forgotten, continues to influence behavior. For example, even though a woman who was raped in an elevator cannot recall any details of the assault, she nonetheless avoids elevators and is unwilling to enter them.
Dissociative amnesia is more common among women than men, usually people who have experienced or witnessed traumatic events, such as physical or sexual abuse, rape, wars, genocide, accidents, natural disasters, or death of a loved one. It may also result from concern about serious financial troubles or tremendous internal conflict (such as feelings of guilt about certain impulses or actions, apparently unresolvable interpersonal difficulties, or crimes committed).
Dissociative amnesia can persist for some time after a traumatic event. Sometimes people appear to spontaneously recover memories.
Unless confirmed by another person or other evidence, how closely and accurately such recovered memories reflect real events from the past may be unclear.