National Sleep Foundation

Chapter 6: Parasomnias

What is a nightmare?

Nightmares are disturbing mental experiences that generally occur during REM sleep (during the later portion of the night) and often result in awakening.1 Occasional nightmares are a normal occurrence.

A nightmare disorder is diagnosed only when nightmares become frequent and significantly affect daytime functioning and mood. Nightmares are associated with limited autonomic activation and can typically be remembered upon awakening—this can help distinguish nightmares from sleep terrors.1


  1. American Academy of Sleep Medicine. The international classification of sleep disorders: diagnostic and coding manual. 2nd ed. Westchester, Ill: American Academy of Sleep Medicine; 2005.