Insomnia is soul-destroying,
we spend a third of our lives asleep. Our attachment to it is instinctive and emotional. We link sleep inextricably with our physical and psychological well-being and we are sure of its curative properties. We tell people who are feeling low: "All you need is a good night's sleep." But we couldn't begin to explain what, exactly, is so good about it.

Scientists can't help. They know what sleep doesn't do; no amount of it can improve your looks. "Experts no longer think sleep is all about body restoration. There's no evidence that it will clear skin up or make hair more lustrous," says Dr Chris Hanning of Leicester General Hospital's sleep laboratory. "In fact, the tendency is for body fluid to be redistributed upwards during the night - so when you wake up your face will be temporarily puffy."

But the scientists have no idea what sleep is actually for.There are theories, of course, but only two things are certain. First, all animals do it. Even cockroaches exhibit periods of rest. Animals vulnerable to predators alter how they sleep rather than trying to do without it; by adopting techniques such as sleeping half the brain at a time, or by sleeping when their predator is awake in order to keep out of the way.

Second, we can't do without it. People cannot be kept awake indefinitely (sleep researchers have tried it), and even short-term sleep deprivation can be dangerous. If you're performing a monotonous task, such as long- haul lorry driving, missing as little as two hours' sleep can prove enough to trigger a fatal mistake. Several recent disasters, including Chernobyl and the Exxon Valdez, have been blamed on workers falling asleep. And on a more everyday level, about 10 per cent of traffic accidents are sleep-related.

It is worrying, then, to find that insomnia is common. In an average night, one in three people (twice as many women as men) will have problems nodding off. For most sufferers, though, the tossing and turning won't last for more than a night or two. "Compare it," says Dr Chris Idzikowski of the British Sleep Society (BSS), "to breathing. Like breathing, sleep is so tightly controlled biologically that most of us will always get enough."

This, however creates its own problems. Precisely because sleep comes so easily to most people, most of the time, there is a tendency to trivialise sleep disorders and a corresponding lack of sympathy for people who suffer from them. Sleep research is taken much more seriously, and is better funded, in the United States. Doctors know alarmingly little about sleep. According to the BSS, 46 per cent of GPs have no training at all on how to deal with sleep-related problems and 90 per cent feel they need more. The BSS is currently working on a five-to-seven-year programme to introduce proper training into medical schools.

"Sleep," Dr Idzikowski says, "has always been regarded - wrongly - as something that can't be controlled. In fact, a lot of sleep disorders can be tackled." Sleeping pills have had a bad press, but most professionals agree that are times when they are just what the doctor ordered.

Ian Hindmarch, professor of human psychopharmacology