Narcolepsy is characterized by excessive daytime sleepiness, symptoms of dissociated REM sleep (sleep paralysis, hypnagogic hallucinations), disrupted nocturnal sleep, and cataplexy (brief episodes of muscle weakness triggered by emotions). Onset of narcolepsy is most often in childhood, peaking between 10 and 25 years of age, and once established the disease is life-long. Significant strides have recently been made in understanding narcolepsy, which can now formally be considered an autoimmune disease based the identification of strong predisposing genetic variants within the HLA and T-cell receptor loci, as well as the identification of increased levels of specific autoantibodies near disease onset.