Scientists believe it could even help people without the condition stay awake for longer periods to meet the demands of a 24/7 society.

Narcoleptics fall asleep without warning, and can include nightmarish hallucinations and paralysing fits that can strike when they laugh, cry or have sex.

Gary Beattie, who suffers from narcolepsy, once worked on a building site.

Gary Beattie says he would try an orexin-based drug if it could give him a normal life

"It was extremely dangerous working on a building site because there have been a few instances where I fell asleep 20 feet up a ladder," he said.

"I just put my back against the ladder, and fell asleep for about 15 minutes."

The illness has had a dramatic effect on his life.

In addition to affecting the work he can do, he has separated from his partner and child.

Bill Baird used to have a high-pressure job as a stockbroker in America's financial industry, until he began suffering from narcolepsy.

Cataplectic attacks would occur every time he was near to closing a deal.

"As I began to establish an emotional rapport with the client, that would trigger cataplexy.

"So it would be a race between whether or not I could convert this person to a client before I converted myself to a lump on the floor."

Obesity

For many years, scientists had no idea what caused narcolepsy.

Sufferers were given drugs to manage their symptoms, including amphetamines, which can have severe side effects.

Then researchers looking at obesity accidentally pinpointed the cause.

Naturally, we would always be asleep, but orexin floods the brain waking us up Dr Jerry Siegel, University of California

Scientists thought a chemical called orexin controlled appetite.

But tests on mice showed those without it were prone to narcoleptic attacks.

Dr Masashi Yanahisawa of the University of Texas who carried out the research, said: "Orexin was not controlling obesity, but it was the first chemical in the brain connected to narcolepsy."

Orexin is present in an area of the brain called the hypothalamus, an area responsible for controlling functions including body temperature and sleeping.

Analysis of the brains of narcoleptics found they had 10% of the cells that make orexin compared to healthy people.

Dr Jerry Siegel from the University of California, Los Angeles, said: "Naturally, we would always be asleep, but orexin floods the brain, waking us up."

This discovery could mean a drug based on orexin could be used to treat narcolepsy.

And if such a drug could be created which had no side-effects, it could be used to help soldiers, surgeons and even shift-workers stay awake for days at a time.

Pressure

Professor Neil Douglas, from the University of Edinburgh said people could do without their eight hours of sleep a night.

"They could enjoy themselves more, see their family more and even work more.

"The 24-hour society would be here. But I think people would get very fed up of constantly encountering other people and being pressured to work 24 hours a day."

Gary Beattie said he would definitely take orexin if it was available: "I'd be really keen to take it, just to find some sort of cure or balance so I can get on with my life and be a normal person again."

Horizon - Living Nightmare will be on BBC2 on Thursday 16 January 2003 at 21.00GMT.