Narcolepsy is a syndrome characterized by profound excessive daytime sleepiness (EDS), which often occurs in association with cataplexy, hypnagogic or hypnopompic hallucinations, sleep paralysis, automatic behavior, and disrupted nocturnal sleep (American Academy of Sleep Medicine 2005). It is subdivided into two types: narcolepsy with cataplexy and narcolepsy without cataplexy. EDS is manifest as an increased propensity to fall asleep in relaxed or sedentary situations or a struggle to avoid sleeping in these situations. EDS may be so severe as to be irresistible, leading to sleep in inappropriate or dangerous situations. Brief naps temporarily relieve the sleepiness in many patients. EDS can lead to related symptoms, including "automatic behavior" (behavior that the individual does not recall), irritability, and poor memory, concentration, and attention. The overall amount of sleep per 24 hours is not increased in narcolepsy. In fact, many patients report fragmented nocturnal sleep, suggesting that the underlying disorder is an inability to maintain any stable sleep–wake state (Guilleminault and Fromherz 2005).