It's become an occupational hazard for celebrities. But what's it really like to live with bipolar disorder?

Gail Porter has it. Stephen Fry made a documentary about it. Sophie Anderton, Adam Ant, Russell Brand, Richard Dreyfuss, Kerry Katona and Tony Slattery are all sufferers. And now Britney, too, has bipolar disorder, at least according to the media, in whose unforgiving glare she has undergone her very public meltdown.

At times, it seems as though bipolar illness is the latest celebrity fad - like wheat intolerance, perhaps. But the apparent spike in celebrity sufferers points to something else: that awareness amongst both clinicians and the public is growing and some of the stigma attached to admitting to mental health problems has begun to diminish.

It is impossible for me to say definitively whether Britney has bipolar. However, there can be tell-tale signs of symptomatic behaviour. Bizarre behaviour such as stripping off in a clothes shop in full view of staff and customers and shaving your hair off are the sort of "crazy" things people do when they are in the grip of mania. But people do "crazy" things for other reasons or if they are having a difficult time - this is what makes bipolar disorder so hard to diagnose correctly.

I used to do some extremely odd things during my manic episodes, when you feel euphoric, disinhibited, full of energy and talk non-stop. Once I went charging back to my school, two years after leaving it. I went bursting into classrooms, interrupting lessons and generally causing havoc. I barged my way into a physics lesson and started pontificating to the class, as my old physics teacher looked on in horror. I did the same thing at a management consultancy I worked at briefly, storming in there and talking excitedly to everyone, a crowd gathering around me.

But the thing about my manic episodes I always found hardest to deal with were the religious delusions. Although I wasn't remotely religious, when at my most ill I thought I was on some kind of mission from God and was going to usher in the Second Coming. I remember seeing God's face in anything and everything. I have since learnt that scientists believe the religious preoccupations associated with mania stem from a part of the brain's temporal lobes that lights up like a Christmas tree with electrical activity, because of the massive over-production of the neurotransmitter dopamine.

It has been suggested that having a celebrity's ultra-outgoing personality might dispose someone to bipolar illness. At least one in 100 people has bipolar disorder. The majority of these are ordinary, everyday people. I find this at the self-help groups run by MDF The BiPolar Organisation (formerly the Manic Depression Fellowship) which I attend. However, there is a huge amount of research suggesting a link between creativity and bipolar disorder. And there have been plenty of people to bear this out, from Beethoven, Byron and Vincent van Gogh to Kurt Cobain. There are two ways of looking at it. If you're mildly manic you bubble over with energy and creative ideas. If you're creative already, the ideas and imagination will overflow. I remember spouting poetry when wandering around the Edinburgh Festival while manic. If I had a gift for poetry, it might have been an incredibly productive phase for me. If you look at Robert Schumann's works, there are years of enormous productivity when he churned out symphonies 10 to the dozen - no doubt when manic. Then when he was depressed, there's nothing.

The celebrity lifestyle, however, might offer other explanations. Chaotic, rollercoaster fortunes, when you might go from "hero to zero", may trigger illness in those who are vulnerable. Drug abuse is a known trigger. Also, cynics might say claiming that you have what seems to be a "celebrity plague" may be a defence, excusing bad behaviour.

I was first diagnosed with bipolar disorder at 19, but I think the symptoms started when I was much younger. I had a normal childhood and upbringing and came from a relatively privileged background, growing up in a middle-class family in the home counties. I went to a grammar school in Amersham, Buckinghamshire, and was a high achiever academically, as well as being very sporty and popular.

But I was a real worrier - and always have been. In my early teens I remember on occasion if I got upset about something it would go on for several days. I still have that now - if something upsets me it feels like the end of the world.

I became more prone to occasional mood swings, which I think were the early signs of illness. I remember becoming tearful for no obvious reason and starting to withdraw when I was in the sixth form. Before university I went travelling for a year, which is when I became seriously ill. Suddenly I started having regular and increasingly severe mood swings.

The scariest thing was that I had no idea what was happening. At the age of 19 most people have never even heard of bipolar disorder - I certainly hadn't. When I was up I'd be enjoying the delicious euphoria, then when I crashed I would rack my brains trying to understand why I was so unhappy. I kept thinking I must have had some terrible childhood experience to make me so miserable, but could never come up with anything. I had no clue that I had a psychiatric illness.

Eventually, in one of the down phases, I gathered the wherewithal to get myself home. By the time I boarded the flight home from Bangkok I was very high. I arrived at Heathrow airport to be collected by my parents. I was talking 10 to the dozen and telling them I didn't need any sleep - when you're really high you really can go without sleep. In a manic week I'd only sleep for an hour or so a night. My family just didn't know what to make of me.

The illness got more and more extreme. The highs were getting worse and I was losing all sense of reality. Instead of just seeming lively and chatty I was talking constantly, my speech became so fast I ceased to make any sense at all. I also did really odd things such as taking photos of people in the pub, or stealing a pint of milk from behind the bar and drinking it.

Eventually, my parents were at the end of their tether. And when you're in the depressed phase, you do realise something's wrong. I went to see my GP and was referred to a psychiatrist. I was seen as an outpatient but it wasn't enough. One day my mum called the GP, who recognised that I was so ill I needed to be treated in hospital. When I was high the GP persuaded me to go to hospital with her - once I was there, I was trapped. They could see I was severely ill and detained me under section.

That was very traumatic. It dawned on me, even though I had nearly entirely lost touch with reality, that I was going to be held there. I was desperate to leave and felt very betrayed by my family. I got into a stand-off with a bevy of burly psychiatric nurses, who surrounded me and had no intention of letting me make a break for the exit.

In the end I was shut in a room while they held the door shut. Eventually they stormed in, pinned me down and forcibly sedated me. The next few days were a blur of heavy tranquillisers that only took the edge off my mania. I still stalked the ward thinking I was either Jesus Christ or the Dalai Lama, and painted the "evil eye" in a manic delirium during art therapy. Because of the unusual nature of my cycling - I was up for a week, then down for a week, where most people have cycles lasting months - after a week I appeared better and was sent home. Of course, I wasn't well, but at least they put me on lithium and another drug, which stopped the cycling after several months. The drugs left me in a severely depressed state, though. I was stuck at home, having lost my place at university and being lumbered with a psychiatric diagnosis. I was struggling to deal with the horror of it all and felt constantly suicidal. After a year I was well enough to attend university, although still very depressed. It took two more years to get my medication right and for me finally to feel OK again. I then did a postgraduate degree in journalism at Cardiff University - which is where I met my wife, Suzanne - and was pretty happy.

But after my course I imperceptibly slid back into depression after cutting back my medication. The next six years of my life were blighted by this low mood. But I didn't even realise I was ill at the time - I thought it was just me. The drugs stopped the cycling but left my mood depressed. I worked as a journalist in various news agencies and, although outwardly I seemed normal, I was crippled by severe anxiety and depression. I then got a job in a Government press office, which I hated, and I just felt so miserable that life didn't seem to be worth living.

Suzanne wanted to get married and have kids. I suddenly realised that if I was going to kill myself it was now or never. I didn't want to leave a bereft widow and fatherless children, so I resolved to take my life. Just after Christmas four years ago I drove into the woods near my parents' house and took an overdose of lithium.

I remember crawling under a tree like a wounded animal to die. As I was lying there I felt God was with me and didn't want me to die. I also realised I just couldn't visit such horror on my parents - it would have ruined their lives, as well as Suzanne's. So I had a change of heart, called an ambulance and was taken to hospital, where they pumped all the stuff out of me.

Ironically, after 11 years with bipolar disorder, that suicide attempt finally enabled me to get proper treatment. For years my doctors failed to see that I was depressed. I was angry with my psychiatrist for not being proactive enough about my treatment - he could have saved me from all those wasted years. But since then they have experimented with my medication. I'm now on the antipsychotic quetiapine, the antiepileptic sodium valproate and an antidepressant, which together seem to work really well.

I still have occasional mood swings, but they're nothing like as severe. I now work for Shift, the Government's campaign against stigmatising mental illness, and recently became trustee of the user-led charity Stand to Reason, which also challenges prejudice towards people with mental illnesses. Recovering has made me want to improve the lot of people like me. I'm happily married to Suzanne, an amazing, long-suffering woman who stuck by me throughout my illness. And we are blessed with two wonderful children, Thomas, three, and Sam, four months.

My heart goes out to anyone in the public eye who does have bipolar. It is an unforgiving illness that makes you behave, both when manic and depressed, in ways that can leave you deeply ashamed when you're in a fit state to reflect on your behaviour.

It is human nature to be intrigued by the peculiarities of our fellow man. But imagine Britney was your sister or someone you loved. How would you feel to see others mocking her? Having a mental illness is no laughing matter, any more than having cancer is. One in seven people with undiagnosed bipolar dies from suicide. Let's give Britney a break.

As told to Dan Roberts

Bipolar disorder: the facts

* Also known as manic depression, bipolar disorder is a mental illness which causes periods of intense depression or mania, interspersed by periods of relative calm. Sufferers experience "cycling", where their mood swings from up to down in a regular recurring pattern.

* The cause is unknown, but it's believed to be an interaction between genes and environmental factors, such as trauma or stress.

* Symptoms of depression include low mood, sleep disturbance, loss of appetite and sex drive, a sense of pessimism and recurrent thoughts of death and suicide.

* During a manic episode, people often experience elevated moods or euphoria, increased activity, speeded-up speech, self-important ideas or grandiose delusions, hallucinations, reduced need for sleep and increased appetite for food and sex.

* About 1 per cent of the population develop bipolar disorder in their lifetime. The risk is much higher if someone has relatives with the disorder, although - about 12 per cent of people with a sibling with bipolar disorder develop the condition.

* There's no cure, but many sufferers benefit from understanding what triggers their episodes and "mood monitoring", which can spot the early signs of a relapse and so avoid it. The main treatment are medications such as lithium, which stabilises mood swings.