Nightmares.

Although sporadic nightmares may be normal responses to stress, chronic nightmares can be troublesome. Nightmare syndrome involves dreams during REM sleep and is associated with abnormal psychologic tests and psychiatric disorders. Night terrors are most common in childhood, occur during deep sleep and rarely reflect underlying pathology. Post-traumatic stress disorder produces recurrent and repetitive nightmares. The onset of nightmares in an adult is often associated with medication or illness.