A flashback is a psychological phenomenon in which an individual has a sudden, usually vivid, recollection of a past experience. The term is used particularly when the memory is recalled involuntarily, and/or when it is so intense that the person "relives" the experience, unable to fully recognize it as memory and not something that is happening in "real time". The medical term for the phenomenon is hypnagogic regression <-SOURCE? (Google only lists other wiki links).
Flashbacks are not necessarily episodic — that is, the re-experienced memories may not include specific identifying features (such as images and sounds) that were part of the original event or experience. Because there is a strong emotional component to memory as well, flashbacks can occur as a rush of feelings, emotions, and sensations associated with a traumatic event. This is especially true for young children who were lacking the cognitive abilities needed to define and characterize the trauma when they experienced it, but who may, nevertheless, relive all of the emotions associated with the traumatic event. In addition, those adult survivors of childhood trauma who have solely these emotional memories to draw on, also may experience them in flashbacks.
When they occur involuntarily, flashbacks may be due to a disorder such as Post-Traumatic Stress Disorder (in cases of war-related trauma, physical or sexual abuse trauma) or Hallucinogen Persisting Perception Disorder (when a person has used psychedelic drugs).
