Night terrors also known as a 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. They should not be confused with nightmares, with are a normal patholoogy of sleep.
However, they can also occur during daytime naps.
In Paternity, the patient, Dan suffers a night terror when he imagines Gregory House entering his room and cutting off his toes. In reality, Robert Chase confirms that Dan's experiencing night terrors.