Nightmare Disorder 405
almost exclusively during rapid eye moveme nt (REM) sleep and can thus occur through-
out sleep but are more likely in the second half of the major sleep episode when dreaming
is longer and more intense. Factors that incr ease early-night REM intensity, such as sleep
fragmentation or deprivation, jet lag, and REM-sensitive medications, might facilitate
nightmares earlier in the night, including at sleep onset.
Nightmares usually terminate with awakening and rapid return of full alertness. How-
ever, the dysphoric emotions may persist into wakefulness and contribute to difficulty re-
turning to sleep and lasting daytime distress . Some nightmares, known as “bad dreams,”
may not induce awakening and are recalled only later. If nightmare s occur during sleep-
onset REM periods ( hypnagogic ), the dysphoric emotion is frequently accompanied by a
sense of being both awake and unable to move voluntarily ( isolated sleep paralysis ). 
Associated Features Supporting Diagnosis
Mild autonomic arousal, including sweating, tachycardia, and tachypnea, may character-
ize nightmares. Body movements and vocalizations are not characteristic because of REM
sleep–related loss of skeletal  muscle tone, but such behavi ors may occur under situations
of emotional stress or sleep fragmentation and in posttraumatic stress disorder (PTSD).
When talking or emoting occurs, it is typica lly a brief event terminating the nightmare. 
Individuals with frequent nightmares are at substantially greater r isk for suicidal ide-
ation and suicide attempts, even when gender  and mental illness are taken into account. 
Prevalence
Prevalence of nightmares in creases through childhood into adolescence. From 1.3% to
3.9% of parents report that their preschool children have nightmares “often” or “always”.