There are two other categories: REM-related parasomnias and other parasomnias. Parasomnias are qualified as undesirable physical events or experiences that occur during entry into sleep, during sleep, or during arousal from sleep.

Sleep terrors usually begin in childhood and usually decrease as age increases. Factors that may lead to sleep terrors are young age, sleep deprivation, medications, stress, fever, and intrinsic sleep disorders. The frequency and severity differ among individuals; the interval between episodes can be as long