Most people's idea of hypnotism is either a steely-eyed Svengali or grown men being dragged on stage and turned into thumb- sucking two- year-olds. Just what Serena Mackesy thought, until she fell under the spell of a certain Mr McKenna ...
Tarantulas have soft hair. Mine seemed to quite like being stroked. She wandered over my wrist and fingers, un-shaven legs placing themselves ever so delicately, like a bird, and then settled in my palm while I caressed her back. She was really sweet.

This may seem normal to you, but I'm still surprised that I petted a tarantula of my own volition. Less than an hour before, I'd watched someone else do it on stage while the sweat coated the palms of my hands. I am, you see, someone who doesn't like spiders. Correction: was. They don't bother me now.

This revolution was wrought in me by a chap called Alnoor, and it was his first go at sorting out a phobia. I'd just talked him into stroking a python. We didn't do this by normal talking, of course: we'd just hypnotised each other.

Hypnosis is a powerful fear-evoker for many people. It's an intimate thing to do to someone without even touching them, especially when the familiar images of the practice are a mixture of Trilby, Rasputin and people with their trousers on their heads. Actually, these images are all quite accurate. Yes, stage hypnotists manipulate people into making fools of themselves. Yes, Rasputin had an unhealthy hold over an unhealthy family. Svengali's release of Trilby's innate talent is perfectly possible. But there is more to hypnosis than tries to avoid the eye.

Increasing evidence suggests that the mind could be one of the more effective drugs in a 21st-century doctor's bag. It has long been acknowledged that placebos can be as effective as real drugs in many cases, but did you know that, in the last century, a Scottish surgeon James Esdaile carried out over 300 major operations, including amputations and the removal of scrotal tumours, using only hypnosis for anaesthetic? A hundred years later, one Andy Bryant not only had a vasectomy while in a trance but walked out of London's Marie Stopes Clinic smiling. Earlier this year, at Kingston Hospital, Surrey, a man successfully underwent a 30-minute hernia operation while hypnotised.

There's more. Among the surgical side-effects recorded are reduced bleeding - Rasputin's reputed ability to control the Tsar's haemophiliac son's condition might well have some basis in truth - and faster recovery times. Studies in America have shown surges in immune system function in post- hypnotic subjects. And as well as stopping people smoking, it can reduce stress levels, quell allergic reactions; even, in some cases, improve eyesight.

What's more, trance is fun. I recently spent four days at a course run by celebrity mesmerist Paul McKenna and his business partner, Michael Breen. This disconcertingly normal duo were teaching a mixed bag of salespeople, corporate trainers, carers, therapists and power-crazed lunatics like myself, simple methods for putting people under. There are several ways of doing this, but nobody swung a watch before someone's eyes all weekend. The most powerful mesmeric tool is the voice: vocabulary, tone and pitch. You talk your subject down, a bit like George Kennedy in Airport.

It was surprisingly easy. I had someone off in about 15 seconds at the end of the first day. I didn't believe it myself. I was certain they were just being polite. But then I put my best friend out during a riotously noisy party, and I knew I was on to something. When she woke up, stretched and said, "Mmm, that was lovely, but if you ever say `empowered' in my presence again I'll sock you," I was convinced.

Contrary to popular conceptions, trance isn't a state of paralysis. It's more a profoundly pleasant state of relaxation, hovering between sleep and wakefulness. Normal distractions like noise, movement, sudden thoughts of red phone bills, fade away. You know you could open your eyes and do something about them, but you'd rather not. Being in a trance is, in fact, a common natural state. "People", says McKenna, "always go, `It's an altered state of consciousness.' I'm not sure what it's altered from. What isn't an altered state of consciousness? Watching television is. Queueing in the bank. Driving a car. Drinking a cup of coffee."

Inducing someone into the state of hypnosis, of course, isn't really the important thing. It's what you do while someone's down that counts. While the conscious mind finds it difficult to cope with several things at once, the unconscious holds everything one has ever experienced, the imagination, reflexes. Access the unconscious mind and you can liberate huge potential. This isn't just a party trick. Over the past couple of weeks loads of my mates have cheered up no end after a session on my sofa.

McKenna is an articulate advocate of his skills. He stumbled into this world himself when, working as a DJ, he was sent to interview a local hypnotist. "I got him to hypnotise me for the show. I felt amazingly relaxed. It was just awesome." Having a talent for showbiz, his growing habit of practising on friends quickly escalated to the stage and then to TV. His TV shows, classic examples of that trousers-on-head style of entertainment, have been a bit of a double-edged sword. Celebrity tends to breed distrust. Then again, it's unlikely that he would have shifted some 500,000 self- help tapes and videos if he weren't on the telly.

When McKenna talks about the work he's done, everything from improving athletes' physical performances to helping a cancer patient manage her pain, he radiates enthusiasm. "I'd like to see hypnosis taught in schools," he says. "It could really help children run their own brains better, not get stressed-out, learn that they've got this amazing computer that they can do things with, memorise things in a fraction of the time it would normally take." Like many advocates, he can go a bit over the top, but I really don't think it's cynical.

Which isn't to say that he's oblivious to the downsides. Without a doubt, hypnosis has been put to unpleasant uses. Anyone who's watched a TV evangelist, or indeed a political rally, will have seen prime examples of hypnotic language in play: repetition, emotive imagery, the insertion of points of potential disagreement into strings of unequivocals. "Hitler was a master of it. He'd talk about the necessity for justice and about God and peace and you'd see people agreeing with him."

There are also many unscrupulous characters out there exploiting the weak. Although, in fact, no one has ever won a case against a stage hypnotist for brain bending - though a woman got damages for a broken leg recently - there is no doubt that vulnerable people have been damaged by hypnotherapists. Then again, quite a lot of people were damaged by Freud. McKenna cites the fact that in America, where hypnosis is increasingly popular as a tool in psychotherapy, 7.5 per cent of therapists admit to having slept with their patients. "Many of those cases where patients have been molested aren't really to do with hypnosis. It's not really that hypnosis has altered their perceptions to the extent where it could take place; it's that drugs were involved. Or these people were extremely vulnerable and the therapist misused the prestige relationship."

In 1995, a businessman won pounds 500,000 in damages from a doctor who drove him to a nervous breakdown by hypnotic experimentation. Closer inspection of the case, though, reveals that the doctor also experimented with massive doses of barbiturates. The field is alarmingly ill-regulated. "The problem," says McKenna, "is that there are tons of these little colleges and journals that set themselves up. One of them I know of has a guy running it who's been inside for GBH and three of its members are known paedophiles. And they've got one of the most convincing-sounding names."

McKenna, meanwhile, is himself embroiled in legal problems. He is currently being sued by a 28-year-old who claims to have been made schizophrenic at one of his stage shows. "I do feel sorry for him," he says. "But actually, the Oxford Guide to the Mind says that schizophrenics frequently believe that they're either controlled by aliens or hypnotised."

I certainly believe I've been hypnotised. And it was great. I've been practising on myself constantly: remembering where I dropped my keys; getting off to sleep - never something I've found easy - at the drop of a hat; sitting in backs of cabs giving myself little endorphin rushes. Obviously there have to be limits to what one can achieve with this lovely skill, but if nothing else, it's going to improve getting stuck in traffic jams no endn

For information on courses (the next is in May), contact McKenna Breen on 0181 340 8089