From the outside anyone would have thought that I was doing pretty well with my life. I'd done well at school, passed my exams, studied medicine and then gone on to achieve the ambition I'd always dreamed of: to become a neurosurgeon, which I did at 26. I really love my work. I'd go into the hospital, zoom around the wards and make life and death decisions every day. Then I'd walk into theatre and perform intricate brain surgery with a team of highly skilled medical staff - my life was just like a gripping television drama.

But what I couldn't explain was why my first though when I woke up was often: "I'm going to kill myself today. I'm going to take a bottle of paracetamol and end it all". I didn't think this was strange - I thought everyone felt like this. But then I'd get up, my mind would fill up with all the things I had to do at work and carry on. No one had a clue how I was feeling. Now, of course, I realise those dark thoughts were the first signs of my mania. I managed to keep going for a while, but I faced huge pressures at work. I had too much to do with not enough time to do everything. I was always anxious about things that were out of my control, such as not having the right equipment, like brain scanners, when they were needed. I was also upset because my brother was getting a divorce. It was particularly hard for me because his wife was my best friend and I didn't want to lose her.

Eventually, I couldn't keep up the front any more. The world had become an incredibly frightening place. I wasn't sleeping, I wasn't eating properly and, apart from keeping clean, I no longer cared what I looked like. But this time, I'd stopped working and all I could do was hid in my flat. I'd moved to Edinburgh to take my job and, because I was doing a 108-hour week, I had no time to make friends, so no on noticed I wasn't functioning properly. My family were miles away and I felt totally isolated.

Manic depression usually follows one of two paths. There are huge highs when you experience periods of hyperactivity, over excitement and elation. Or the opposite may be true, when your moods are mostly black and full of deep despair. For me, it was like being caught in a very bad scary movie. The neighbours had gone away, so there was no one around me, but I kept hearing noises, and at the slightest creak I'd hide under the covers. I ripped all the telephone wires out of the wall because I was sure the place was bugged. When you're in that state, everyone and everything becomes a threat. If the paperboy looked at me, I htoug he was sinister. Even an old coke can chucked on the path became significant, and I drove myself crazy wondering why it was there. I trusted no one. I was hopeless, totally off the wall.

The next thing I can remember is a doctor coming to my flat. Then the police arrived, which is routine but terrified me. I was sedated and taken away in an ambulance. For a while I didn't know where I was. My head felt like it was full of putrid soup with all these vile chemicals swilling round. I was completely out of it. But even in my drugged and dazed state, there were things happening that were really humiliating. All I had were the clothes I stood up in - I couldn't even get a toothbruch for a week. The nurses control everything. I was watched all the time - even whne I was in the bath, and if there wasn't a female nurse around I'd have to lie there in front of a man.

One minuted I was a top surgeon, and the next I was shut in a hospital room right at the bottom of the pile. I was always the clever one, the successful one - this wasn't part of the plan at all. When, after a few days, my parents arrived I felt so deeply ashamed I could hardly face them. No one's sure why manic depression develops. About a fifth of sufferers have a parent with the condition, but the rest, like me, don't have anyone in the family who's affected. But there things don't come from nowhere and they don't happen to happy sorted people. Everything was going wrong, but I didn't realise and I careered out of control. Personally I think there are lots of causes. A stressful lifestyle, an unhappy childhood, or you just can't cope very well. We have such huge expectations of life - we're all supposed to be successful. Manic depression often seems to hit high achievers, which definatley applies to me. I'm bouncy, enthusiastic, but when a crisis comes, I plummet. I now know it's not compulsory to work 24hrs a day - there are other things. It's definately not compulsory to be the greatest neurosurgeon in the world.

But my life is so different now. The high-flyer career has gone. Instead, I work as a GP two days a week, and the rest of the time I do things I enjoy. I think most people looking at me would find it hard to believe that 13yrs ago I was a patient in a psychiatric ward. When I was forcing myself up the ladders, I was so wrapped up in my work there was no time for relationships. One of my colleagues at the hospital I used to talk about his wife and I can remember thinking he was odd - it seemed such an irrelevance. But now that I'm married to a lovely man, I understand the importance of having someone to love. At first I was nervous about revealing my past to my husband. But, eventually, I plucked up the courage and let it out, bit by bit. He took it all in his stride which was wonderful.

These days my mental health is my absolute priority and if anything conflicts with that, I don't do it. People who get problems often can't say no. I used to keep taking on more and more and get hugely stressed. Now I say no to people even if it means letting them down - there's no way I'm going to let myself get ill again. I've finally worked out the trigger that tips me over the edge. There's always a build-up and I've got a whole check-list of things I look at regularly, before things spiral out of control. Alarm bells always go off if I stop sleepoing. The happens before a low. So, now if my husband says I look tired, I listen. Having someone who loves you is very healing. I've got a good handle on myself now - it's all about knowing and living within your limits.

There's one sadness though. I'm 43 and would have loved to have had children, but I know it's not to be. I could get ill again, and that would be bad for any child. We have talked about it and decided we are happy as we are. It's now several years since my last episode. I'm still a bit over the top and life to rush around madly, but that's me. When I wake up in the morning I feel fine. The turning point for me came after my third breakdown, when I found myself on a special ward for hospital staff. The beds were full of doctors who'd had breakdowns and it was a revelation. Suddenly I realised I wasn't alone. Doctors work such crazy hours, with so many pressures on them all the time, it's hardly surprising they get sick. Thirty percent of doctors are depressed at any one time, and the suicide rate is high. The other doctors I met were terrified of being honest about their problems, and we all discovered we had no one to talk to. So that's why I helped set up Doctors Support Network - it's a special website where doctors can talk to each other, discuss their problems and get information from other high-level doctors.

More than anything I want to lift the taboo on mental illness. I never told anyone I'd been in hospital, and I was terrified of people finding out because I thought I'd be shunned. But, eventually, I decided to come out about myself, being honest is the only way to change attitudes and get rid of the stigma that surrounds mental illness. Now when I meet people I say yes, I've had episodes of depression, but I'm fine. They can see I'm a happy person, leading a normal life, and they accept it completely.

I take the mood -stabalizing drug Carbamazapine, but it's managing my moods that has made the difference and now I'm probably far easier to be with. I was incredibly scathing and if someone couldn't do something I'd think: "What an inferior human being". Now I think: "Maybe they can do stuff I can't, and who cares?". All sorts of people may have times when they can't cope. I hope they will look at tme and see it doesn't have to be the end of the world. You can get better and lead a normal life.

Liz set up a website Med4u. A panel of experts will answer questions on any problem, from skin rashes to breast cancer. Consultations cost £25 and replies are given in around 48hrs.