flashback

Short definition from Wiktionary

Noun

1. 1
   A dramatic device in which an earlier event is inserted into the normal chronological flow of a narrative.
2. 2
   A vivid mental image of a past trauma or other sensation that the trauma is happening in the present, especially one that recurs.
3. 3
   A similar recurrence of the effects of a hallucinogenic drug.
4. 4
   The condition of the flame propagating down the hose of an oxy-fuel welding system.
5. 5
   A query that operates against data from an earlier time, before it was changed.

Verb

1. 1
   To undergo a flashback; to experience a vivid mental image from the past.