It's around midnight and I'm lying awake, finger on my pulse, afraid to go to sleep in case I never wake up.

I'm not having palpitations, but I'm uncomfortably aware of my heartbeat and the physical presence of my heart in my chest. Should I phone a friend or dial 999? What if it's a false alarm and I end up spending hours in A&E for nothing, like I did last time? The chances of burning to death in your sleep are apparently one in 10,000 (am I alone in thinking that's worryingly high?) but the only odds I can find on dying from a heart attack in your sleep are "very little". So why have I spent so many nights checking my heart rate and worrying whether I'll still be here in the morning?

My chronic anxiety was first diagnosed more than 20 years ago, when I started having panic attacks on the tube, but looking back I'd say I was almost certainly an anxious child. I just didn't know the name for the uneasiness I would often get in my stomach, the sensation of blood pounding in my head and my fear of falling asleep at night, afraid I might stop breathing if I wasn't awake to monitor every intake of breath. As I got older, the anxiety attacks got worse. And then, in August 2005, I really did stop breathing: I had a cardiac arrest.

I had just turned 50. The previous night and that morning I had been doubled up with chest pains that had been diagnosed as heartburn several weeks earlier and which turned out to be angina. After breakfast I'd gone to the bathroom to get myself ready for lunchtime drinks with friends. Shortly afterwards I called out to my partner of the time, Jim, that I was going to faint.

By the time he reached the bathroom, I was lying on the floor. At first he assumed I had just fainted but he soon noticed that I wasn't breathing and that my skin was waxy. A black triangle was forming between my chin and chest, where the blood was racing to get to my heart. Only it couldn't get to my heart because a blocked coronary artery had gone into spasm, and my heart had gone into ventricular fibrillation. I was clinically dead.

I am unbelievably lucky to be here. During a cardiac arrest blood stops circulating to all parts of the body. A lack of oxygen to the brain causes you to stop breathing, with brain damage almost certain if you are not resuscitated within about five minutes. I skirted as close to those five minutes as you would dare. Only 2% of people survive sudden cardiac arrest and early defibrillation is the only effective treatment for ventricular fibrillation, where your heart goes into a flurry of rapid, chaotic electrical activity that is ultimately useless. As luck would have it (although I tend to come down on the side of miracles these days), I lived a three-minute ambulance drive away from the hospital and the paramedics arrived to kickstart my heart in the nick of time.

I don't remember any of this. In fact, I remember very little of the two weeks sandwiching the event. Initially, I was somewhat piqued to have missed one of the major episodes of my life. I would have liked to report back something mystical from the front lines - white lights, a bearded guide or an angel, a sense of peace - and I couldn't believe I had missed paramedic Joe in his aviator shades, who even Jim said was gorgeous, enacting a scene from ER in my bathroom.

But that lack of memory turned out to be something of a blessing at first. For a couple of months I couldn't accept that I had come alarmingly close to death, the advantage being that I didn't for a moment worry about it happening again. For someone who can have an anxiety attack while making a cup of tea, this was truly liberating. But it wasn't long before anxiety started to creep back in, only this time I had something real to worry about. Pre-cardiac arrest, I didn't worry about actually dying because I had never had a serious illness, and I certainly wasn't anxious about developing a heart problem because there was no history of heart disease in my family. Now I was staring in the face of the ultimate anxiety - I might die without warning.

When it came to establishing the possible causes of my blocked artery, none of the doctors or consultants I saw had pointed a finger at anxiety. To be fair, it's difficult to isolate any one factor and anyway, I ticked all the usual suspects - high blood pressure, high cholesterol, cigarette smoking, cocaine use, too much saturated fat. Alcohol was in there too. It's not thought to cause coronary heart disease, but in excess it will almost certainly cause your blood pressure to rise, which can.

I gave up fags and coke and cut back on booze. Most days I went for a brisk 30-minute walk. I even changed my diet, although there's only so far you can travel along the road of self-denial without becoming a bore and I refused to replace butter with low-fat spread. And then, earlier this year, I started getting palpitations for days at a stretch, even though I'm on beta blockers, which are designed to regulate the rhythm of your heart. Palpitations can be scary enough, but when you've had a major cardiac event they're panic-inducing. In my case it feels like my heart is missing a beat. The space between beats is interminable and the next beat comes in with an almighty thump. It's like having an arrhythmic percussionist in your chest.

Pumped up with stress, I lurched from one panic attack to another. Sometimes they'd be triggered by an actual event; when a freelance copywriting job was cancelled at the last minute I spent an entire weekend so wired I couldn't sleep and my insides felt as if they were trying to crawl out of my skin. At other times, the anxiety seemingly came from nowhere. Putting on my makeup I'd notice the increasingly unpleasant sensation of butterflies that signals an attack; my limbs would feel as if they had lost all substance and I'd become light-headed, disorientated and short of breath, my lips and tongue would tingle and I would break out in a sweat. When I had my first panic attacks in my mid-20s, I thought I was going mad. Even now, when I know they will end, I'm afraid that this time I might unravel completely.

The discomfort and distress of the combined palpitations and anxiety were so acute I ended up in tears at my GP's clinic and was referred back to the cardiac unit. So far the consensus seems to be that the palpitations are caused by anxiety. Very little research has been done into the links between anxiety and heart disease, but a recent study found that chronic anxiety was a stronger risk factor in developing heart problems in men than any other psychological factor, including those attributed to the archetypal heart attack victim - the type A personality who is driven, overworked and explosive. And women are more prone to anxiety to men.

Even more reason to lie awake at night. But what's the solution? I've tried meditation, autogenics, exercise and cognitive behavioural therapy, which sometimes alleviate low-level anxiety but don't touch the sides when I'm spiralling out of control. Anxiety medication is notoriously habit-forming and I already pop more pills than I used to at my most hedonistic. John Steinbeck allegedly used alcohol to ease intense bouts of anxiety. Believe me, it's tempting. With a few glasses of rioja inside me I'm calmer, happier, more at ease with myself and the world. Plus, it's fun, which is something you lose sight of when you're gripped by anxiety.

I'm not saying I want to be completely laid-back. For one thing, I'm prepared to concede that a certain amount of tension might be creatively beneficial to a writer. But there are times when my anxiety is so severe I think being addicted to Valium would be child's play by comparison. What bliss to wake up without feeling anxious about being anxious, worrying about how many years my anxiety is knocking off my life, and to fall asleep without wondering whether I'll make it through the night.

• Lorna Thorpe's poetry collection A Ghost in my House is published by Arc, priced £8.99.

Do you have a story to tell about your life? Email it to my.story@theguardian.com. If possible, include a phone number.