Sufferers, who are seized by an instantaneous and overwhelming desire to sleep, have been known to slump into their soup at dinner parties, snooze through meetings, and even drift off during sex.
On the roads, they put themselves and others at risk by falling asleep at the wheel. Daytime sleepiness caused by narcolepsy and other sleep disorders is the commonest cause of fatal car accidents.
It is an inherited condition whose cause is not understood, although there is growing evidence that it is linked to a disorder of the immune system. One of the worst features is a sudden loss of muscular control, called cataplexy, whenever a sufferer becomes excited. The effects include shaking of the jaw, slumping of the head and buckling of the legs.
Dr Meryl Dahlitz says: "You make a joke, hit a good shot at tennis or get angry, and you collapse. Anything that suddenly increases the level of alertness can trigger an attack. It is socially disabling."
In the UK an estimated 40,000 people are affected, but only 3,500 have been diagnosed. Stimulant drugs, based on amphetamines, help keep some sufferers awake during the day, but they tend to develop tolerance, requiring increasing doses, with a greater risk of side effects.
Kathryn Appleby, 32, has suffered from the condition since she was 18 but was not diagnosed until she was 25. She would drop off in discos or on country walks if she sat down for a rest. If she laughed or got excited her knees would weaken, her jaw would drop and her eyes would roll. But she couldn't persuade her GP to take an interest.
"It is hard to convince people of how much you are actually sleeping. I then changed doctors and was referred to a consultant neurologist. He said I was a textbook case of narcolepsy."
Now married, with two children, she is being treated with drugs which have successfully controlled her condition. "I am lucky - not everyone responds so well. But I missed out on so much before I was diagnosed."
Michael Sergeant, chairman of the UK Narcolepsy Association, says sufferers typically delay for years before seeking help, and are then dismissed by GPs who tell them to buy a bigger alarm clock or go to bed earlier. "It is totally humiliating. For each of us who has been diagnosed there are another 10 out there struggling along, not knowing what is wrong. They are fobbed off by being told there is nothing wrong with them, or they are given the wrong diagnosis or treatment"n
The UK Narcolepsy Association , 1 Brook Street, Stoke on Trent, Staffordshire, ST4 IJN (01782 416417).Reuse content