I can't say exactly when it started. Maybe the day in July last year when a headache in the shape of a question mark curled itself around my right eye and made itself at home. Or a month later, when a liquid fatigue poured into my legs and set. The autumn perhaps, when short, surreal episodes would come and go, like I was seeing the world through the bottom of a highball glass.

But the moment when I really knew something was wrong was the night of my 40th birthday party in October. We were motoring up the Thames with a boatful of my closest friends all dressed in 1969 fancy dress and Woodstock wigs. I felt overwhelmed. From under my Jimi Hendrix hair I whispered to my mother, "Stay close." I gripped her hand as if it were the first day at school. I couldn't look anyone in the face for more than three seconds without a tide of screaming panic rising up. I tried to circulate but needed to sit. When I sat, I needed to stand. I tried eating, then threw my dinner in the bin. At last midnight came and we all went home. That night, for the first of many dark nights, I lay awake, small and frightened, and utterly unable to keep still through the dreadful hours.

It got worse. For two weeks I felt neither ill nor well. Then, during a weekend at my parents' home – the house I was born in, the place I still love – I disintegrated. It was the weekend the clocks went back, and as we arrived I rippled with a sense of unease. I couldn't watch television or read. I started cups of tea but couldn't finish them, sat down to dinner but couldn't eat. The first night I roamed around, twitchy and unable to settle, heart hammering in my throat, ears full of white noise, a buzz in my stomach. At 5am, I couldn't take any more. I knocked on my parents' door and soon found myself wedged between them in bed, for the first time since I was born. The next night was worse. I was rocking back and forward, ranging, pacing, terrifying everyone. When I blurted out something about how it was all finished for me, my dad jumped into the car to find an out-of-hours NHS dispensary. "At least we're making the most of the extra hour," he said.

They used to call it a nervous breakdown. Now it's depression. Neither term is helpful. The former doesn't come close to expressing the long list of symptoms that apply (insomnia, anxiety, dismal mood, panic, thoughts of suicide, loss of energy/weight/joy/libido/love). The latter is, if anything, worse, conjuring up misleading images of people staring through windows at drizzle. But depressive illness isn't like that Monday-morning feeling, or getting back from holiday to find the cold water tank has burst. It's a medical fact, like breaking an arm, only the broken bit is in the chemical circuitry of the brain. It's delicate stuff in there. It takes a long time to fix. Usually, I am told, you get better.

If there was one consolation it was that I was not alone. My decline from unremarkable working dad of three to stranded depressive sitting on the floor doing simple jigsaws certainly felt unique. In fact, it's universal. The chances of the average adult getting it are perhaps higher than they have ever been.

According to Graham Thornicroft, a professor of community psychiatry at the Institute of Psychiatrists, between 20% and 25% of adults will have an episode of mental illness in any given year. Over a lifetime, the risk rises to around 40%. In Britain, antidepressant prescriptions have doubled in the last decade. The World Health Organisation warns that by 2030 depression will be second only to HIV/Aids in the toll it exacts on society.

"Life has become more stressful and there is more alienation than there used to be. People who meet disadvantage meet it very much alone," says Tim Cantopher, a psychiatrist and author of Depressive Illness: Curse of the Strong

Who's most at risk? "Women and poor people," says Thornicroft. "General rates of depression among women are up to twice as high as among men. And in lowest socio-economic groups it is up to twice as much as in higher groups."

I fit neither category, so why me? Depression is often triggered by sudden life events such as bereavement, loss of job or change of house. But again, none of these apply. Far more common however is a stress-induced condition that may build over a number of years.

"If you try to do the undoable, you're going to get this," Cantopher says. "Stress doesn't make you ill. You do – by trying to do the undoable."

And, if I'm honest, I have been trying to do the undoable for years. I have realised I am essentially an idle soul inhabiting a very busy person's life. Years of late-night shifts and early mornings with small children asking tricky questions such as, "Daddy, if you had to break one of your legs, which one would you break?" I was a "portfolio parent", part-time work, part-time homedad, part-time freelancer. On paper, it looked marvellous. In reality, it made for long years of chaotic breakfasts, a messy school run, some exercise, a dash into London, 10 hours on a pinball newsdesk, back to release my wife for a school governors' meeting or a conference call or to move the house slightly to the left. Late for everything.

I understand that this is the lot that many working women have had to bear for decades. I find it unsurprising that so many are succumbing to depressive illness. But since I "came out", I found a startling number of do-it-all fathers who are suffering too.

Mark Rice-Oxley in his Hendrix gear at his 40th birthday party – the point when his depression took hold.

And yet not many of us find it easy to be forthcoming about our illness. Thornicroft's real killer stat is this: that 75% of us know someone with mental illness. But we may not know they are mentally ill. Because, of course, mental illness is a taboo. And few people talk about it or let on – unless they are so ill that they can't help it.

Sue Baker, director of the Time to Change programme set up to change negative attitudes towards mental illness, says nine out of 10 people with mental illness say they have experienced stigma and discrimination. "Yet, paradoxically, 'coming out' can be the best thing for someone with a mental illness. It can have a powerful influence," says Baker. "If you don't disclose, then people who might help you aren't going to be able to."

I tried to be honest and, in return, people did well at asking all the right questions. How has it been? What's it like? Why did it happen to you? In the interests of brevity, I usually just said "Pretty tough" or "I'm on the mend" or "not out of the woods yet". What I really wanted to say is: there were days when I just sat on the bed and stared at the wall and wondered if I was losing my mind, when even trying to do a child's jigsaw puzzle would wear me out. Days – long joined-up hours when I thought I would never work, write, parent, play or love again. Days when I agonised at the enormous burden my wife was under; when I resented the impact on my children, two of whom seemed to develop mild sympathetic symptoms; when I wondered how much further there was to the bottom. But the days weren't the problem. Nights were worse. Sleeplessness became both symptom and cause of the illness, a wicked loop of empty hours and catastrophic thoughts. By 4am I'd be desperate for dawn. But morning brought no relief, just more empty hours, with another threatening night thereafter.

Christmas was the lowest ebb. All that snow, all the lovely children with faces shiny like apples. I couldn't be near them, but couldn't be alone. I trailed around the house after my poor wife like a small dog with internal bleeding. I slept eight hours in four nights. On 23 December, I went for an emergency meeting with my psychiatrist who shook his head and said, "I'm sorry it's turned out this way." Afterwards, in the thickening twilight and with the first vapours of sedation gathering, I felt my wretchedness in the joy of others: the shoppers and their gift bags; the lovers giggling; the young man on the tube engrossed in a book. I wish I was him, I thought. I wish I was engrossed in a book on the tube.

How do you get better? Like wars and love affairs, depression is a thing that is easy to get started but difficult to bring to a close. Somehow, time passed. Days dragged by so slow, but weeks seemed to mount up quickly. The lost time began to unsettle me, so I found different units to measure the duration of my illness: in haircuts, porridge boxes, Countdown octochamps. Any kind of stress was insupportable. But also any kind of excitement. Television could overwhelm me. I couldn't watch sport, felt seasick at the motion and envious of the energy of the participants. Small social events helped, but only for about half an hour. Thereafter diminishing returns set in, and they diminished pretty rapidly: if you overexert in any way, very bad days follow. I spent hours and hours with a deck of cards, and camomile tea, and got pretty bored of both.

The four things that really helped: meditation, love, time and therapy. I discovered the first through a colleague who sent me some CDs. At first, meditation feels hard and slightly odd. In time, it's a valuable technique. Love – in a child's Halloween face, or a friend's casual invitation to lunch, boosted morale. Time worked away on the broken bits. Therapy taught me that I'm not who I think I am, that some of my reflexes and instincts are unhealthy.

But it wasn't a smooth ride. Some days, exercise would help. Some days, it was too much and I'd suffer for two or three days. Some days, odd jobs felt wholesome, sometimes they felt depleting. Some days, just making dinner would be too much. Other days, I would feel like doing nothing, but know that doing nothing was the worst thing I could do. Some days, most painfully of all, being with the children was just too much. At other times, just to sit and watch them climb or paint was a blessed relief. I could still parent, after all.

"Be a scientist, not a manager," says Cantopher. "Look at the evidence that your body gives you. If you are overdoing it, your body will tell you. You've got to pace it in the early stages. To begin with, do a little – leave tasks half done, don't try to complete things at the beginning. Be kind and gentle to yourself. Once you are better, then it's about recognising that if you keep putting 18 amps through a 13 amp fuse, it will keep blowing."

Spring helped. I got stronger. I finished reading a novel for the first time since September. I put on all the weight I'd lost and more. I planted potatoes, cooked, sifted compost, borrowed a neighbour's bike. I kept a nerdy graph of how I was feeling, and took comfort in a general upward trend behind the violent peaks and troughs. Good friends brought lunch and we walked and talked. The office sent a box set of The Wire. Pretty soon I was up to watching it. I began to notice things more, things I had taken for granted for years – beauty, seasons, people. I bought birthday presents on time. I rediscovered gentle ways to spend the time – chess, libraries, yoga. I learned how to let time pass without trying to fill it.

It wasn't straightforward. I relapsed six weeks after going back to work and needed another month to build up from the bottom again. Even now, a year on from that first, dark question mark, I still feel the sharp edge of something. But, happily, it does little more than prod me, remind me that I need to tread carefully.

I wouldn't wish this illness on my worst enemy; it's the most terrifying thing that has ever happened to me. But, in a strange way, I am glad of the lessons it taught me. "A lot of patients are grateful," says Cantopher. "They say that without the illness they wouldn't have been able to make the changes they made to become happy."

It has been strange writing this story. Almost like I am writing about another person. A friend died the other day at 44. My story seems trivial by comparison. But it is a story I really wanted to tell because it is a story I wanted to read 12 months ago, when I was desperate for reassurance. Yes, it's tough, yes, it'll turn your life upside down. But it does get better. You do recover. I've nearly made it. You can make it too.