Parasomnias are undesirable physical, behavioral or experiential phenomena that occur during entry into sleep, within sleep, or during partial arousals from sleep. Depending on their exact manifestations, frequency and intensity, parasomnias can be considered normal sleep phenomena, especially when occurring during childhood, and may not significantly impact sleep quality or quantity, or daytime functioning. While some parasomnias (e.g., recurrent isolated sleep paralysis, sleep-related groaning) may cause relatively little enduring distress, others (e.g., nightmares, REM sleep behavior disorder, sleepwalking, sleep terrors) can have significant consequences, including marked psychological distress, self injuries and sleep disruption in the patient and a mixture of concern and apprehension in family members.