When Serena Davies decided to go on a meditation holiday in Thailand, she didn't get a cushy few days in a luxury spa, with joss-sticks, massages and plenty of sleep. Instead she battled with her inner-self, fasted and fought off cravings for banana pancakes.

Wat Ram Poeng is a monastery and meditation centre and was my home for four weeks. A gorgeous array of temples and holy spaces, amidst flower beds and fountains, it is perched at the edge of Chiang Mai, Thailand's second city and a far more pleasant climate and urban base than the exhausting, polluted Bangkok.

Foreigners as much as Thais are encouraged to come here and learn to meditate. In fact, the quarters set aside for farangs (as we are known) are so much in demand that those of the Thais are being usurped. Everywhere are wan figures, dressed in the obligatory white, walking like zombies, eyes staring at the ground as if searching for a lost contact lens, or writhing in painful approximations of the lotus position, faces composed in a severe serenity.

They are practising the walking and sitting meditations of the Vipassana Technique, one of the oldest and purest strands of Buddhist meditation - which, advocates claim, is the original technique that Buddha devised. The only demand Buddha made of his followers was that they practise meditation, for, he said, this is the direct path to enlightenment. No worshipping of graven images and no prayers to gods unseen.

The farangs at Wat Ram Poeng meditate for seven, eight or nine hours a day if they are newcomers, a daunting 12 or 13 if they are into their third week. We rise at 4am, can't eat after 12pm, can't sleep before 10pm, can't listen to music, can't read, and certainly can't snog, go raving or call their mummies when it all gets too much. No lollipops here, just hard hard work.

So why do it? Vipassana meditation is "insight" meditation. It teaches mindfulness. It teaches that if we try at each second to be aware of ourselves, our thoughts, our emotions, sensations and desires, we may achieve a better understanding of reality.

But it isn't depressing. As you get a little more skilled at the job - 12 hours of practice a day assists miraculously - you react less to thoughts and feelings, you cease to generate more, and begin to be taught by those that are there.

Most farangs stay for 10 days, which is an extremely good innings by anyone's standards. But the full retreat offered at Wat Ram Poeng lasts 26 days, and there is something at its end called "determination". We called it "detention" as a joke, but it's actually rather worse. Determination requires that the student stay awake for approximately 80 hours - three full nights - and meditate the entire time. (Don't worry, I failed).

Little precious snatched breaks for a cup of coffee or a yoghurt drink are allowed, but basically you are left to meditate for 19 or 20 hours a day. Food is brought to your room, but curtains are to be kept drawn, and escape is solely permitted for your daily visitation to the teacher. You aren't allowed to wash, you aren't allowed to change your clothes, and you aren't allowed to brush your teeth. This is hardcore. They just about stop at putting you under lock and key.

I always knew it was coming. It had been my whole reason for going. The drama appealed. But on the first night reality overwhelmed me: What on earth was I doing? How could I possibly have the stamina, precious middle-class me, with my pre-requisite nine hours sleep a night? Did I really want to make myself terminally ill and incurably insane? Staring at the blue tiles in my cell until they danced before my eyes, half listening to the Thais chattering outside until they seemed suddenly to utter English phrases. I was sure I heard one offering me a cup of tea. And wasn't she my mother?

Every time a door banged I shook. I was variously adorned in woolly hat and blanket or stripped to my bra at the slightest fluctuation in temperature. At night, unable to sit on my bed due to the creaking sound it made, I crawled around my room on my hands and knees so as not to wake the others in adjacent rooms. As a result, the trousers I was forbidden to remove rapidly became the colour of mud, and my limbs were filthy.

This was turning into a horror film. It had to stop. It was neither big nor clever. Twenty-four hours into the exercise, heart pounding down to my toes, I lay down on my bed and gave up. I wept with relief.

I awoke an hour later, responding to some deep-buried pang of guilt. Excellent, I remembered, I was free. I could be in the glittering metropolis of Chiang Mai a whole two days earlier than planned. I could call my boyfriend and be treated to the incoherent babble of the latter part of his Friday night. I could eat banana pancake TOMORROW.

Stumbling outside into the heady combination of sunshine and other human beings, I met a friend. I proclaimed my liberation. He looked at me aghast. "You know what they say about the marathon," he said, "It's a twenty mile warm up and a six mile race." Was I really going to give up now?

I went to my teacher confused. Ajan Suphan is one of the most respected monks in the whole of Thailand, Buddha-like, amid the swathes of orange silk he never removes. Faced with such an image of sagacity, telepathy and absolute equanimity, I knew that announcing my obstinate, overriding desire for a banana pancake had simply ceased to become an option.

I left his room with the second day's instructions in my hand.

And so followed the most surreal, or should I say real, night of my life. The restlessness ceased, my mind miraculously refocused and remained so for 15 still, silent hours as I walked and sat through the night. I lit my room with rows of candles, which dripped profusely over my makeshift altar of buddha and trinkets and along the cracked skirting where I walked.

I watched as I became drowsy, I watched as the drowsiness passed away. I watched the hunger turn to completeness - with no sustenance. I watched impatience melt to rest. And at 7.45am I stopped thinking. I don't exactly know what happened then and I certainly don't want to proffer a story of epiphany here. All I know is that something took place, for about an hour, that made all the suffering - ever - feel worth it. And it was something to do with not thinking.

Wat Ram Poeng teaches people how to meditate. What you choose to learn is up to you.

Every night I would venture a few metres outside the monastery to buy hot sweet soya milk in a plastic bag from the smiling matron at her battered table and bubbling cauldron. I learnt to spin rubber bands round the bags just like her, and close them with a flick of the wrist. I think that's the only certain lesson I can say I take away with me. But that is a good thing.