Narcolepsy usually begins in the late teens or early adulthood, although it does sometimes develop later in life. Unfortunately very little is understood about the disorder, which is characterized by occasional lapses into the deepest stage of sleep, the rapid eye movement (REM) cycle. While most people spend around an hour and a half sliding through three lighter stages of sleep, narcoleptics enter it almost immediately. This is generally accompanied by excessive daytime sleepiness, hallucinations, disrupted nocturnal sleep, and cataplexy, in which the body is overcome by weakness.
In cases of narcolepsy in tandem with cataplexy, a lumbar puncture can be used to discern the cause. To perform the lumbar puncture, a long needle is inserted between the lower back (lumbar region) vertebrae, drawing out cerebrospinal fluid, which can then be analyzed. Low levels of hypocretin, a chemical the brain emits to help the body stay awake are connected with cataplectic narcolepsy.
Narcolepsy itself, however, is often very difficult to pin down to one cause. There is a slight genetic component—about ten percent of people with narcolepsy and cataplexy have a family history of the disorder. Sometimes the lack of hypocretin is caused by a genetic mutation that reduces hypocretin production. So while people with narcoleptic family members are statistically more likely to have narcolepsy themselves, the likelihood is much lower than it is for other diseases that are nearly always a result of genetics.
Rare cases have been noted where injuries to or tumors on the part of the brain that is involved in REM sleep are considered to be at least part of the cause of narcolepsy. Hormonal changes during puberty (and sometimes menopause) can also trigger the onset. According to the National Institute of Health, “infections, exposure to toxins, dietary factors, [and] stress” are other factors that can play a role in the development of narcolepsy, as can extreme changes to sleep schedules (such as switching from working day shifts to night shifts).
All in all, the brain remains quite an enigma. Researchers still understand comparatively little about the brain, sleep, and sleep’s effect on the brain, thus risk factors are more easily identifiable than the actual cause of the development of narcolepsy.