It's not exactly known to the sleep disorders community what particularly causes narcolepsy. It's know that it's a dysfunction of the hypothalamus which is a part of the brain that's thought to regulate sleep and wakefulness. The way I was taught to see it, in my time working at sleep disorders, is to imagine a series of light switches and the switches are what in the brain regulates us for sleep and wake and in people with narcolepsy these switches are set wrong and tend to mis-set themselves throughout the course of the day and night. It's also been found in research with animals that a hormone in the brain called hypocretin is at a deficiency in dogs and cats who experience narcolepsy, but that study hasn't been carried over to humans yet and it's not yet known the role of hypocretin in human narcolepsy. They have theories that hypocretin is involved, but there's no treatments based yet upon this theory. Narcolepsy does have genetic connections to it, especially narcolepsy with cataplexy. We can use a blood test to look for a genetic marker which appears in a percentage of the population that has no narcoleptics, no narcoleptic symptoms, but in narcolepsy with cataplexy we find the genetic marker in sixty percent of patients.