The prevalence of sleep terrors in the general population is unknown. The prevalence
of sleep terror episodes (as op posed to sleep terror disorder, in which there is recurrence
and distress or impairment) is approximately 36.9 % at 18 months of age, 19.7% at 30 months
of age, and 2.2% in adults. 
Development and Course
NREM sleep arousal disorders occur most co mmonly in childhood and diminish in fre-
quency with increasing age. The onset of sl eepwalking in adults with no prior history of
sleepwalking as children should prompt a search for specific etiologies, such as obstruc-
tive sleep apnea, nocturnal seiz ures, or effect of medication. 
Risk and Prognostic Factors 
Environmental. Sedative use, sleep deprivation, sl eep-wake schedule disruptions, fa-
tigue, and physical or emotional stress increa se the likelihood of ep isodes. Fever and sleep
deprivation can produce an increased freq uency of NREM sleep arousal disorders. 
Genetic and physiological. A family history for sleepwalking or sleep terrors may oc-
cur in up to 80% of individuals who sleepwal k. The risk for sleepwalking is further in-
creased (to as much as 60% of offspring) when both parents have a history of the disorder.
Individuals with sleep terrors frequently ha ve a positive family history of either sleep
terrors or sleepwalking, with as high as a 10-fo ld increase in the prevalence of the disorder
among first-degree biological relatives. Slee p terrors are much more common in monozy-
gotic twins as compared with dizygotic twins.  The exact mode of inheritance is unknown.
Gender-Related Diagnostic Issues