Narcolepsy is a sleep disorder that makes you feel excessively tired and, in severe cases, have uncontrollable sleep attacks, making it extremely dangerous. Sleep attacks can come on at any time—eating, walking, or driving. Many people with narcolepsy don’t know they have the sleep disorder. Sometimes it can run in families, but in most cases, it is not genetic. Other sleep disorders that result in daytime sleepiness are often misdiagnosed as narcolepsy. Sleep apnea, circadian rhythm sleep disorders, and restless leg syndrome all cause daytime sleepiness.