EVEN though I finished covering the siege of Sarajevo 14 years ago, for years the town and its people, trapped between the mountains and the snipers, haunted me. The memory that dominated was of two old ladies I'd met while I was a war reporter in the city. I could not forget my final meeting with them, when their second winter of war had sent them raving mad with cold and fear. And in my turn, I was overwhelmed with guilt that I had been unable to protect them.

To this day I don't know what happened to them. I hope they survived, but I have been unable to find out and my mind won't allow me to remember. For me, those two old ladies were one of the abiding memories in my five-year fight with post-traumatic stress disorder (PTSD). Even though they weren't my responsibility and I only met them three times, I felt I should have saved them.

Now it is all a long time ago but, like most people involved in the war in Bosnia, I was deeply relieved last week to see Radovan Karadzic, the former Bosnian Serb president, dragged blinking from behind his bushy-bearded double life as an alternative therapist, under arrest and on his way to a war crimes trial.

Not only is he responsible for ordering the deaths of an estimated quarter of a million people during the war from 1992-1995, the majority of whom were innocent civilians, but also, as a psychiatrist, he must be only too aware of the enormous mental legacy his war has left.

Now they call it post-traumatic stress disorder, but its old name is survivor guilt syndrome and it is a theme of my semiautobiographical Sarajevo novel, The Girl in the Film, published last week.

I often used to dream I was being machine-gunned, and, finding it hard to connect with my London life, desperately sought out people I knew in the war. I remember feeling that more than anything I wanted to be normal - to have the families and babies that were enveloping my friends. But I couldn't seem to work out how to change gear. The most overwhelming feeling, however, was that of guilt: unlike the trapped population of Sarajevo, I had been free to come and go, to eat and drink, and had failed somehow to care for the two old women.

I was very young when I first witnessed war - 26 and straight out of Oxford. I got my degree results while on assignment in Bosnia in 1992 on my way to see the Serb concentration camps. I spent my days talking to half-mad skeletons, halfstarved women and children weeping, packed in their thousands into school gyms-turned-refugee camps, desperate to know where their men had gone. At the time I thought only about them, and about telling their story. It never occurred to me that their wretchedness would sink into my brain. And if I had known, it wouldn't have stopped me: PTSD is an illness with a delayed reaction - it takes time before you realise what is happening to you. My real PTSD trigger was the Kosovo war a few years later in 1999. I could not return to the Balkans to cover the conflict as I had ruptured a disc, so could not wear aflakjacket.Instead,Icommutedbetween my newspaper office and a talking head's sofa on the BBC News, being the only journalist left in London who knew anything about the Balkans.

It was a different war, but Slobodan Milosevic's mind was behind it and the Serb police uniforms were the same. When the war was over, I kept bursting into tears. When I started rocking backwards and forwards in front of Dad's Army, screaming: "They would have all died, died!", it was time to seek help.

The symptoms of PTSD are probably best described by Professor Slobodan Loga, professor of psychiatry at Sarajevo University. During the war, he told me that all the Sarajevans would go mad after it, as would the journalists; we would be cracked mirrors for the rest of our lives. I am certainly not the only journalist to suffer from it. It was the rank injustice of the siege which was so hard to bear. And, perhaps, our ability to nip in and out of the war on UN planes while the population had to hunker down, to be shot and starved. Many journalists were affected - some are now dead of drugs, drink or suicide. Some, like me, have retired from war reporting, or faced their demons in other ways. Others are just very weird. Almost the weirdest are those who say the war had no affect on them at all.

Nor is it just journalists - soldiers, aid workers, it hits us all. It is very common in anyone who has been exposed to traumatic events such as bombs or train crashes. During the First World War it was known as "shell shock" or "battle fatigue" when identified in soldiers who had survived the trenches. It can also affect the victims of muggings, people who have been beaten up, or witnessed a car crash. And the symptoms may take more than a decade to emerge.

Professor Loga lists the symptoms of PTSD as violent mood swings, becoming easily excited, flashbacks, memory loss, nightmares, predilection to drug and alcohol addiction, emotional numbness, depression, anxiety attacks and trying to find someone else to blame (very common, he says, among the military).

But for me, for some reason, my last meeting with those two old ladies was one of the most traumatic things I did. I don't why - perhaps it was the shock. If you are going to see a mass grave, or a rape camp, you are geared up for it in advance. But nobody had prepared me for two women who had gone mad.

I first met them in August 1993. Sarajevo had been under siege from the Bosnian Serbs for 17 months - a modern European city of 400,000 at the mercy of the soldiers on the mountains that penned the city in. By then I was The Observer's permanent correspondent in Sarajevo.

It was almost impossible to get food and medicines in Sarajevo at the time, so when a Bosnian doctor in London asked me to take back some medicines for his ageing cousins, I agreed. I hired a driver to take me up the sniper-raked street where the old women lived - it was far too dangerous to do the 20-minute walk. They lived on the third or fourth floor of one of the sprawling concrete estates opposite Sarajevo's mortuary; two Muslim ladies, Old Sarajevo's ruling elite, smartly dressed, in shirts, linen skirts and sensible shoes, still wearing their rings, but very thin: they had been on starvation rations for over a year.

THEIR flat, like everywhere else in Sarajevo, had no electricity and smelt slightly of urine because the mains water and power had been cut off by the Serbs. They were also very afraid, not just because of the bullets they faced when they sneaked outside to fetch water, or the shells that monotonously crumped into the surrounding streets, but because one of their sisters had died of cold and hunger the previous winter.

In the baking August heat, their repetition: "Winter is coming. Winter is coming," chilled my soul. Another winter with no electricity or gas, let alone food and water, and the glass blown from their windows, in a city where temperatures regularly reach -10C or worse, could kill them both. I promised I'd visit them again but I didn't come back until November. I had other families I had adopted in town. I'd been travelling to other parts of Bosnia and home to London, plus it was very dangerous to go up their street.

By November, they were cold and even more scared, and their jewellery had vanished. I gave them some food - not much, as food was hard to find: a cabbage was nearly £15 and coffee cost £45 a kilo. I swore I would return. But days dribbled past, and I flew back to England. When I next returned, I'd lost their address.

It was March before I saw them again, the day before I was due to go back to London. Snow lay thick on the ground and the two old ladies had gone completely mad - they were raving at me, incoherent, insane. My interpreter and I were stunned with shock.

There had been a ceasefire, and a pizza parlour had managed to open. We got them a £20 pizza and I gave my interpreter as much cash as I could and begged her to look after them, to buy them some wood for their stove, some food. But I'd been in Bosnia for months and was down to my last 150 Deutschmarks. We both knew it wasn't enough and my interpreter had her own family to look after.

I don't know if the ladies died or not. They probably did, although life did get easier for most Sarajevans after that spring. But whenever I tried to talk about them, I would start rocking backwards and forwards and clawing my face. Logically, whether they died or not, it wasn't my fault, but logic plays little part in this. Anyway, it's a blank. I blanked out a lot of things in Bosnia - another common symptom of PTSD. I said to a BBC journalist during a whisky-fuelled evening that everyone assumed I had seen terrible things when in Bosnia, but actually I hadn't seen anything very bad. He looked at me as if I were mad, and said: "But you were in that hospital in Mostar in 1993!" I retched: "Oh God, I'd totally forgotten."

My mind had wiped out the earth-hewn, candlelit cellar, which served as a hospital on the River Neretva, as Croat artillery thumped down. I'd forgotten the 12-year-old girl who had moved her hand down to cover her private parts when the doctor lifted the blanket to show us the amputations he'd done earlier - except that she no longer had a lower arm or hand to cover herself. They had been blown away by a shell while she'd played with her brother that afternoon.

Many years later, in 2004, I spent six months in Sarajevo researching the postwar section of my novel, and I went back to see Professor Loga. He told me the suicide rate had gone up since the war by 40 per cent. And as for a cure: "PTSD is part of our lives. What else can you expect of people with the kind of social problems we have?"

I am luckier than Professor Loga, who exhibited pretty much every symptom of PTSD when we met, because I am much better now - although for my first few weeks in post-war Sarajevo every time I stared up at the mountains where the Serb snipers used to be, my heart leapt and I was terrified of being shot. There was a point at which I thought that if the therapists took away my irritability, mood swings, addictions and an inability to maintain close relationships, I'd have no character left. But, after three years of lying on a sofa saying: "I feel so guilty," I'm much improved.

Writing my book was cathartic because I had to relive the entire war. It was like getting into a very mouldy fridge and scrubbing it out. Luckily, my fridge is a lot cleaner now, albeit with a few smears left. I can't stand fireworks; deserted streets can have me wondering where the snipers are hiding and when I see my old colleagues from Bosnia, we tend to get blind drunk. The rest of the time I'm very sober and I've even managed to have a boyfriend or two.

The key was given to me by an Auschwitz survivor I met once. He told me about the death march in January 1945, as the SS emptied Auschwitz in the face of the Russian advance. "The Germans were shooting the stragglers at the back," he said. "I was only 19 and I was helping this old, old man to walk: he was only 35 but he was old. We got nearer and nearer to the back. Finally, one of the SS guards said: 'If you don't want to get yourself killed, get your arse up to the front of this line.' So I left the man. And I heard the shot. You have to live with that for the rest of your life but I did not shoot him and I did not start the war. "

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