A friend's somnambulations may be the cause of, but for those whose nocturnal activities lead to self-injury or assault, there is little to laugh about. Abigail Rayner reports
Think "sleepwalking" and an unfortunate pyjama-clad individual will wander, arms outstretched, across your mind. The popular image of the sleepwalker is one of a humorous nature, accounts of which make comical, after-dinner conversation. Admittedly, tales of people entering a public bar wearing nothing but a dazed expression and urinating over the resident dog are cause for some amusement, but the other side to sleepwalking - the cases of death and serious injury - aren't quite so funny. For many, sleepwalking is a disease with highly serious implications, which, at best, is a worrying disorder and, at worst, a killer.

Joe has been sleepwalking for as long as he has known how to walk and even he chuckles slightly as he recounts the tales of his night wanderings. But his affliction has been the cause for some pretty close calls.

"My parents tell me that I used to get out of my cot while in a sleepwalking state and that, as a little boy, I had to sleep with them so that they could grab me when I started to wander off.

"I used to sleepwalk two or three times a night. It's caused me some fairly major problems. I fell out of a second-storey window on to a patio. Luckily, my body was so relaxed I didn't break any bones, and I just picked myself up and rang the door bell. But I did have a big gash in my leg and I had to go hospital."

Chance is often the saviour of the sleepwalker - not least in the case of the 34-year-old man from Torquay who awoke to find himself clinging to a cliff edge, 40ft above the sea. As luck would have it, it was a calm night and his cries for help were heard by a neighbouring household. Some are not so fortunate, however, such as the 13-year-old boy on a skiing holiday in Switzerland who plunged to his death after climbing out of a hotel window.

The dangers of sleepwalking, however, are not confined to the walker, as Rob, an habitual sleepwalker, well knows. "I've punched my girlfriend and left a big bruise on her arm, and I even threatened to cut off her head," he admits.

"I didn't like to go away on trips for fear of what I might get up to, but on one occasion when I did go away with a friend, we went to sleep in the same room and I awoke to find myself holding an ashtray poised ready to hit this guy over the head. Thank God, something had jolted me out of my sleep - I could have killed him."

There have been many recorded instances of sleepwalkers attacking others, some of which have led to criminal charges. In 1994, a 29-year-old prison officer from Newcastle-upon-Tyne claimed to be sleepwalking when he forced his way into a young woman's house before dragging her into a bedroom. He did not rape her but uttered his wife's name, got up and went home. He was charged with burglary with intent to commit rape and assault, but his plea of not guilty on the grounds of temporary insanity was accepted when the judge heard from experts that sleepwalkers cannot control their actions.

Not all offending sleepwalkers walk free from court since judges also have the option of confining them to a psychiatric ward. Nor is a defence of sleepwalking always conceivable: in a rape case it would not be accepted because, while a sleepwalking man can do all manner of complex things such as drive a car, ride a horse or kill his mother-in-law, he is unable to have an erection.

The reason that aggression is directed at others by sleepwalkers is due to another element, says David Nutt, Professor of Pharmacology at Bristol Royal Infirmary - the "night terror", which tends to go hand in hand with sleepwalking.

"Night terror causes the person to feel assaulted and therefore they might lash out at others," says Professor Nutt. "I had a case of a young man who shared a tent with a friend in some woods. During the night he thought he was being attacked by a bear and tried to strangle it to defend himself. Unfortunately, the 'bear' was, in fact, his poor friend.

"The person's ability to act on his fears in this way separates night terrors from nightmares: during nightmares muscle paralysis will prevent the person from moving, but during night terrors paralysis will be absent."

Despite the potential danger in sleepwalking, little help is available to sufferers. Joe, who was consistently sleepwalking until the age of 30, visited his GP with some regularity but there was little he could do.

"The doctor always prescribed me tranquillisers. They didn't help at all and just made me extremely over-tired. I eventually became so tired that I started falling asleep at work, so I went back to the doctor and asked if there was anything more he could do. He gave me some new sleeping tablets. I'd sit on the bed and take them with a cup of tea, and that would be the last thing I would remember - I'd wake up in the morning fully clothed."

The traditional method of treating sleepwalking is by psychotherapy and low-dose benzodiazapines, which are tranquillisers, or the anti-depressant drug impramine. Benzodiazepine is thought to suppress slow wave sleep during which sleepwalking is more likely to occur. Impramine is thought to ease anxiety, which is a possible cause. For many, however, this form of treatment has little effect and only results in lethargy.

The problem is that no one really understands what causes sleepwalking and, as a result, treatment has been quite limited. "We know that sleepwalking is genetic, it runs in families and it affects more children than adults," says Peter Fenwick, a consultant neuropsychiatrist at the Institute of Psychiatry. "It is what is known as 'a state transition disorder' - that is, where the transition from slow wave sleep to dreaming sleep does not run smoothly, but we don't know exactly what causes it. Sleepwalking can be triggered by several things such as emotion, tiredness, alcohol and drugs, prescribed or otherwise."

It is obvious that what is needed is more research and the finance to back it. Professor Nutt is shocked at the lack of NHS funding in this area. "We are one of very few sleep disorder clinics of this kind in the country and ours is run completely on research funds and not NHS money. In Britain, 20 per cent of a GP's visitors complain of some kind of sleep problem and 5 million people in Britain use sleeping pills. It is a highly neglected area of medicine, and it's a very serious problem."

Professor Nutt's enthusiasm was good news to Joe: when he eventually found help in the form of Bristol's psycho-pharmacology unit things really started to look up for him. "For the first time in my life someone was interested in my problem. They came to my house and wired me up to a monitor which tested my brainwaves when I went to sleep. Following the tests they prescribed me Paroxetine, which stopped the sleepwalking straight away."

Sue Wilson, a researcher at the clinic, explains why the results were so immediate. "The treatment that Joe has been prescribed is a selective re-uptake inhibitor, usually used in the suppression of panic attacks or as an anti-depressant. The only difference is that it takes two to three weeks to take effect with those conditions, whereas with sleepwalking and night terrors it works after just one dose.

"We don't know why it works, but it produces changes in serotonin - a chemical transmitter in the brain - which could be the key. So far, we have only tried the drug on seven patients, but four of them have seen their sleep problems completely abolished and the other three have encountered a substantial reduction in symptoms.

"The next step for us would be to do a controlled study in which we withdraw half the patients from the drugs and try to get some consistent results. We are constricted by funds, however, and there are none available to carry out the study."

For Joe, relying on medication is a worry. "I never wanted to be on drugs permanently. I see them as a sort of sticking plaster that covers up but doesn't really heal, but I'd be a bit frightened of coming off them now because I'm so much better."

Until such time as funds become more available, however, that prospect is not very likely. Meanwhile, Joe is grateful he no longer has to rely on luck and an understanding girlfriend to keep him out of trouble and in his bed.