Narcolepsy is a rare but serious condition that can be very disabling, affecting the ability to drive and to work for many people (although many people with narcolepsy do work). Narcolepsy can cause the person to spontaneously and uncontrollably fall asleep, and may be accompanied by cataplexy (a loss of tone in the muscles causing the body to become limp). This can happen without warning or can be triggered by a shock, or by laughter.
Often people think they have narcolepsy when there are other problems causing excessive sleepiness, but excessive sleepiness is just one symptom of narcolepsy and can have other causes such as allowing insufficient time to sleep, circadian rhythm disorders, or poor adaptation to shift work. One common cause of excessive sleepiness which should be investigated is sleep apnoea.
On the other hand narcolepsy is also often not recognised and people can live with symptoms for years before diagnosis.