406 Sleep-Wake Disorders
Culture-Related Diagnostic Issues
The significance attributed to nightmares may va ry by culture, and sensitivity to such be-
liefs may facilitate disclosure.
Gender-Related Diagnostic Issues
Adult females report having ni ghtmares more frequently th an do adult males. Nightmare
content differs by sex, with adult females tend ing to report themes of sexual harassment or
of loved ones disappearing/dying, and adult males tending to report themes of physical
aggression or war/terror. 
Diagnostic Markers
Polysomnographic studies demonstrate abrupt awakenings from REM sleep, usually during
the second half of the night, prior to report of a nightmare. Heart, respiratory, and eye move-
ment rates may quicken or increase in variab ility before awakening.  Nightmares following
traumatic events may also arise during non-REM (NREM), particularly stage 2, sleep. The typ-
ical sleep of individuals with nightmares is mild ly impaired (e.g., redu ced efficiency, less slow-
wave sleep, more awakenings), with more frequent periodic leg movements in sleep and rel-
ative sympathetic nervous system activation after REM sleep deprivation. 
Functional Consequences  of Nightmare Disorder
Nightmares cause more significant subjective distress than demonstrable social or occu-
pational impairment. However, if awakenings are frequent or result in sleep avoidance,
individuals may experience excessive daytime sleepiness, poor concentration, depression,
anxiety, or irritability. Freque nt childhood nightmares (e.g.,  several per week), may cause
significant distress to parents and child.
Differential Diagnosis
Sleep terror disorder. Both nightmare disorder and sleep  terror disorder include awak-
enings or partial awakenings with fearfuln ess and autonomic activation, but the two dis-
orders are differentiable. Nightmares typically occur later in the night, during REM sleep,