<unk> , also called sleep<unk> , is a sleep disorder causing feelings of panic or dread and typically occurring during the first hours of stage 3–4 non-rapid eye movement (NREM) sleep and lasting for 1 to 10 minutes. It can last longer, especially in children. Sleep<unk>  is classified in the category of NREM-related parasomnias in the International Classification of Sleep Disorders. 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<unk> s usually begin in childhood and usually decrease as age increases. Factors that may lead to sleep<unk> s 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 as weeks and as short as minutes or hours. This has created a situation in which any type of nocturnal attack or nightmare may be confused with and reported as a<unk> .<unk> s tend to happen during periods of arousal from delta sleep, or slow-wave sleep. Delta sleep occurs most often during the first half of a sleep cycle, which indicates that people with more delta-sleep activity are more prone to<unk> s. However, they can also occur during daytime naps.<unk> s can often be mistaken for confusional arousal. While nightmares (bad dreams during REM sleep that cause feelings of horror or fear) are relatively common during childhood,<unk> s occur less frequently. The prevalence of sleep<unk> s in general is unknown. The number of small children who experience sleep<unk>  (distinct from sleep<unk>  , which is recurrent and causes distress or impairment) are estimated at 36.9% at 18 months of age and at 19.7% at 30 months. In adults, the prevalence is lower, at only 2.2%.<unk> s have been known since ancient times, although it was impossible to differentiate them from nightmares until rapid eye movement was studied.
Night terror
Sleep paralysis
Night Terror
Biovail
Bad Trip
Youth suicide
Copycat suicide
Yumiko-chan incident