Psychogenic amnesia (also known as functional or dissociative amnesia) is a disorder characterized by abnormal memory functioning not caused by any structural brain damage or known neurobiological source. It is characterized by retrograde amnesia or the inability to retrieve stored memories and the memories leading up to the onset of the amnesia (especially those that are of a traumatic or stressful nature). It is also characterized by the absence of anterograde amnesia or the inability to form new long term memories.
Two types of psychogenic amnesia exist: global and situation-specific. Global amnesia, also referred to as fugue state, refers to the sudden loss of personal identity, lasting for a few hours or days. Though fugue state is very rare, in most cases, patients will lose their autobiographical memory and personal identity but are able to learn new information and function normally. Situation-specific amnesia occurs as a result of a severely stressful event either experienced or witnessed.