From: Stanford School of Medicine's Center for Narcolepsy
Cataplexy, a pathological equivalent of REM sleep atonia unique to narcolepsy, is a striking, sudden episode of muscle weakness triggered by emotions. Typically, the patient's knees buckle and may give way upon laughing, elation, surprise or anger. In other typical cataplectic attacks the head may drop or the jaw may become slack. In severe cases, the patient might fall down and become completely paralyzed for a few seconds to several minutes. Reflexes are abolished during the attack.