Louise Spicer was 14 and going through an emotional crisis when she had her first out-of-body experience (OBE). 'It was my first night in Australia,' she recalls. 'My parents had split up and they'd packed me off to spend Christmas there with relatives. I was tired and slightly jet lagged. I'd gone to bed and was lying there thinking how strange everything was; I was trying to sleep but my mind was buzzing.

'Suddenly I felt pinned to the bed and, at the same time, had a horrible, stomach-churning sensation of being thrown around the room, up the wall and on to the ceiling, where I was looking down on myself. I'd lost the physical power to move because of this strange pressure on my body. I was trapped. It was the most terrifying feeling.' Now a 21-year-old student, she believes she could still undergo the same frightening experience - if she allowed herself to.

Out-of-body experiences - in which people have the sensation of leaving the physical body for a short time - are now being taken seriously in academic circles: this summer Oxford University awarded its first doctorate for work on OBEs to Charles McCreery, a research officer at the Institute of Psychophysical Research in Oxford. OBEs, Dr McCreery reports, are more common than people think: 20 per cent of the population experiences one at some point in their lives, usually in their teens and early twenties.

OBEs should not be confused with near-death experiences in which patients also report sensations of leaving their bodies. Scientists believe that these experiences are likely to be caused by changes in brain chemicals that occur before such people are resuscitated.

Dr McCreery's research was based on two groups: 200 who had never had an OBE and 406 who had. Part of the project consisted of a personality questionnaire to measure hypomania - the ability to experience heightened excitement or arousal. He found that his OBE subjects scored significantly higher for this than the control group.

'The people who did not score highly tended to be placid and phlegmatic and they tended not to have OBEs,' Dr McCreery says. 'The ones at the top had the big mood swings. They were the worriers, the creators, the ones most likely to suffer bouts of depression.' The fact that OBEs are most common in the 15-25 age group, he believes, ties in with the findings about hypomania. 'When you're young, you are passionate and emotional. There are these big swings of mood. The older you get, the more stable your nervous system becomes.' The feeling tends to occur when someone is physically relaxed but their mind is active.

Melvyn Bragg could not bring himself to reveal his teenage OBE terrors until he was 48. In the novel he wrote then, The Maid of Buttermere, he says: 'It happens to me usually when I am alone and may be associated with fear of solitude or with that greatest fear of all . . . Death. It is as if a distinct part of - is it my soul? - leaves my body entirely and completely, totally and unmistakably - hovers above it looking back on this vacated thing of flesh, bone, blood, breath, water, matter.'

Bragg developed strategies to combat his fear: 'You make yourself very tired so that you go to sleep right away, you find certain noises that will stop you thinking it could happen because if you started thinking it might happen, it would happen . . . You'd go to bed and this thing would just slip, or you'd look in the mirror and it would slip, and you'd think: 'How can I put myself together again?' '

Dr McCreery says he has met many people with 'an absolute terror' of not being able to end the experience. 'It stems from the fear they could be stuck 'out there' forever or die in the middle of it,' he says. 'But if, instead of struggling to 'get out', they could relax and stop worrying, the thing would probably end spontaneously.'

Not all out-of-body experiences are so scary. A professional flautist had one while giving a recital, says Dr McCreery. 'She told me that, from a mechanical aspect, she played better than usual, technically flawlessly, but that her playing lacked emotional interpretation.'

Melanie Benton, 34, was walking down the street when she experienced one. 'One moment I was hurrying along, the next I was high in the air gazing down on myself and people below. As I stopped at the kerb and looked both ways before crossing the road, I noticed that the parting in my hair was not even at the top of my head, giving the appearance of a tiny bald spot. This created a shock of indignation and within a flash I found myself walking along again, inside myself this time. Nothing like this had ever happened to me before.'

Dr McCreery also discovered that those who'd had more than five OBEs became curious as to what triggered the experience and would try to induce them, using meditation. The ability to meditate - a state in which the subject is physically relaxed but mentally alert - is, he says, related to a tendency to have OBEs.

One of his most interesting discoveries was that the OBE subjects were almost twice as likely to be migraine sufferers than the control group. 'It makes sense, doesn't it?' he says. 'Migraine is very much a disorder of arousal. It starts with this period of hyper-excitement or a sense of tremendous well-being; then comes the pain, you go into the slump and then you come out of it.'

Alice Wells, a 22-year-old student, has suffered from migraine attacks since she was a child. Then at 14 she also started to have out-of body experiences.

'You're at that volatile age when you're not old enough to push the feeling away, but not young enough not to be aware of it,' she says. 'It's like a ghost of yourself haunting you from somewhere above and, because you're so scared of it happening again, it does happen - over and over . . .'

Now she is able to control the sensation, although her unease about it remains. 'Sometimes, mostly late at night when I'm in bed, I feel something in myself begin to slip. Now I know that the answer is to press the remote control button and fill the room with the comfort of television.'

Dr McCreery stresses that having an OBE need not be traumatic. To anyone who is worried, his advice is to stay calm. 'If you are lying down, distract yourself by getting up, walking around and finding someone to talk to. Best of all, try not to worry: if possible adopt the attitude of a detached observer. Persuade yourself this is a neutral and interesting experience.'