A night terror, sleep terror or pavor nocturnus is a parasomnia disorder, causing feelings of terror or dread, and typically occurring in the first few hours of sleep during stage 3 or 4 non-rapid eye movement (NREM) sleep. Night terrors tend to happen during periods of arousal from delta sleep, also known as slow-wave sleep. The prevalence of sleep terror episodes has been estimated at 1%-6% among children and at less than 1% of adults.