A Flashback is a phenomenon in which a person has a sudden, intense recollection of a past experience. The experiences recalled are often traumatic in nature, and are so vivid that the person having the flashback relieves the experience. While infected with a virus that disguised itself as a memory engram, Tuvok suffered from flashbacks of himself as a child, holding on to another child hanging over the edge of a cliff. The Doctor soon discovered the virus, and used radiation to eliminate it from Tuvok's system. (VOY episode Flashback).