Parasomnias are disorders characterized by abnormal behavioral or physiological events occurring in association with sleep, specific sleep stages, or sleep-wake transitions. Unlike dyssomnias, parasomnias do not involve abnormalities of the mechanisms generating sleep-wake states, nor of the timing of sleep and wakefulness. Rather, parasomnias represent the activation of physiological systems at inappropriate times during the sleep-wake cycle. In particular, these disorders involve activation of the autonomic nervous system, motor system, or cognitive processes during sleep or sleep-wake transitions. Different parasomnias occur at different times during sleep, and specific parasomnias often occur during specific sleep stages. Individuals with parasomnias usually present with complaints of unusual behavior during sleep, rather than complaints of insomnia or excessive daytime sleepiness.