发作性嗜睡病（Narcolepsy），又名猝睡症、渴睡症，是一种睡眠障碍，与睡眠机制相关的异常。最早是由美国史丹佛大学的附属医院发现。

病人普遍在日间有无法用意志控制的渴睡情况出现，一天可能好几次，有时更会在没有预警之下（连病者也不知道）而突然昏睡或猝倒。而且跟夜间的睡眠时间无关。而摔倒是因为对肌肉控制能力的短暂性丧失。时间可以从几秒到长达几分钟。这段时间，患者的意识完全清醒却连一根手指头都动不了。这种失去肌肉控制能力的症状的原名是Cataplexy，是嗜睡症的附带症状。通常出现在患者情绪突然转变的时候，比如笑，生气，惊讶或害怕。这种病遍及世界各地，不分年龄种族。但很多学生往往被误认为是爱在上课时睡觉的顽皮学生，而得不到应有的关注及治疗。而成年患者却容易把这种病的症状误解成压力或睡眠不足。

Narcolepsy is a chronic neurological disorder involving the loss of the brain's ability to regulate sleep-wake cycles. Symptoms include excessive daytime sleepiness, comparable to how people who do not have narcolepsy feel after 24–48 hours of sleep deprivation, as well as disturbed sleep which often is confused with insomnia. Another common symptom of narcolepsy is cataplexy, a sudden and transient episode of muscle weakness accompanied by full conscious awareness, typically (though not necessarily) triggered by emotions such as laughing, crying, terror, etc. affecting roughly 70% of people who have narcolepsy.