Flashback
A flashback was an episode in which a person suddenly relived their memories of a past experience. Flashbacks could be caused by a medical condition known as hypnagogic regression or simply a traumatic incident. ()

Nog suffered several flashbacks involving losing his leg in a Jem'Hadar attack on AR-558. ()

Lieutenant Tuvok suffered flashbacks to a false memory created by a virus masquerading as a repressed memory engram. A mind meld with Captain Janeway resulted in a flashback to the time Tuvok served on the  under Captain Hikaru Sulu. The virus that infected him was transmitted to him then by science officer Dimitri Valtane. ()

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Psychological conditions