During my visit to Uganda I spoke to a lot of sick people, but I spoke most to three: Christine, Gladys and Moses. And there was also Aida, the girl who wasn't ill, the girl who wasn't going to die but instead would have to take on huge responsibilities.

The girl who was nurturing a mango plant.

I have already written about Christine. A few miles from her house lived Moses. I had made a few notes on the overnight flight from London, but when I looked at them later, the questions I had written seemed idiotic. The most idiotic of all was: "When did you start being afraid?"

It was the most obvious question, of course. Fear, open or concealed, affects everybody suffering from a fatal disease. You keep waiting for test results that can turn out to be a death sentence.

A young man who tested positive for HIV in Gothenburg at the end of the 1980s told me how the doctor who had to inform him of the positive result burst into tears. He was nineteen when he discovered that he was infected. Instead of trying to cope with his own fear, he found himself having to console the weeping doctor.

When did you start being afraid?

When had I been afraid?

During the night I spent on the flight from London to Entebbe, I thought a lot about the occasions in my life when I had been paralysed with fear. I could recall three situations in particular, one of them was when I was waiting for news from a doctor.

I was in Mozambique, it was autumn, the days were hot. I was working on the production of a play, but started to feel unwell. I suspected it was influenza, possibly malaria, or it could simply be exhaustion. As usual, I had been working far too long hours. The tiredness wouldn't go away. I dragged myself as far as my Renault 4 in the mornings and sat there, having long, silent conversations with myself before making up my mind to try to work one more day.

But then one morning, when I reached the theatre and had parked the car, I stayed behind the wheel. It was obvious that there was something badly wrong with me. I was seriously ill, something nasty had found its way into my body and was threatening my life. I drove home again, but stopped on the way to buy some food. As I went up the steps I bumped into Christer, a Swedish dentist and aid worker.

"You're completely yellow," he said.

I went to my doctor, who sent me to a clinic for tests, and I returned with liver readings that were nothing short of catastrophic. I was sent at once to South Africa. I remember nothing of the journey. But it was an aggressive form of jaundice. (I suspect it was caused by a dirty salad at a restaurant in Pemba in northern Mozambique.)

But it wasn't only jaundice. One morning a doctor came to see me. He was obese and was wearing a Jewish skull-cap. I remember my messengers over the years very clearly, all the people who have passed on to me vital information.

I did not know his name, but I remember there was sweat on his forehead as he told me, without beating about the bush, that they had found a patch in one of my lungs. It could be ominous. It would take several days for all the test results to come through. Then he went away. I don't think he had looked me in the eye once during the brief time he was in my room.

I remember the feeling of paralysis that gripped me. Panic was a sharp hook stabbing into my consciousness and immediately sending signals to all parts of my body. Fear makes itself felt in the stomach as well as in the brain. It was like a frantic telegram being rattled out by a machine inside me.

Lung cancer. I hadn't avoided it.

I smoked my first cigarette at Spencer's cafe in Borås, in Allégatan. It must have been one of the last days in August, 1963. I had just started secondary school. One of my classmates, a girl called Hedelin I think it was, offered me a cigarette. A Prince. I had never smoked before, apart from a couple of furtive puffs on stumps of cigars in Sveg. But now I felt obliged to accept the cigarette. From then on I was a smoker. Although I had long since stopped smoking by the time that Jewish doctor came into my room, all those packets of cigarettes had caught up with me. Followed me all the way down to southern Africa. I had stopped smoking too late. Lung cancer was going to kill me. I could envisage my lungs covered in lumps of tar. In desperation, trying as far as possible to keep the panic under control, I tried to convince myself that I might be able to live for a few more years. Not more than a few, probably, but long enough to have a chance of completing some of the things I had planned. Not ten books, but maybe two. And a play, if I really worked hard.

There followed a few days of extreme panic. I lay in my sickroom, sometimes listening to the sound of gunfire in the unsettled Johannesburg night; the fear came and went in waves. I don't recall ever starting to cry, though. I stopped short of that. It would be a defeat already if I went to pieces. In that case the illness would be let loose and finish me off immediately. I tried to imagine the number of days in which I would be able to lead a normal life in spite of everything. I tried to convince myself that the cancer had been discovered very early and hence I would have a considerable way to go before my last journey.

I lay awake at night, hoping the whole thing might be a mistake. A technical fault in the X-ray machine, a piece of dust on the plate.

One morning the obese doctor with the skull-cap came back. I gripped the bed frame tightly and prepared to listen to my death sentence. But he informed me that it was an accumulation of fluid in one of my lungs. Nothing dangerous, not cancer, nothing to worry about. Then he was gone.

I wonder what he knew about people's fear. Perhaps it was beneath his dignity to worry about such lowly human emotional reactions? I thought afterwards and I still feel that I hate that man for his inability to recognise my fear. But what about me? Do I see the fear of others when it ought to be obvious?

Both my other two moments of well-founded terror are associated with incidents in Africa. Late one night in Lusaka I was attacked as I parked the car outside the house where I lived. I was dragged out of the car by a man with blood-shot, drug-crazed eyes. He held a pistol to my head. I still don't know how long it was there. I have tried to reconstruct how long it would have taken the bandits to pull me from the car. Thirty seconds? More? Less? I don't know. But I was quite certain that I was about to die. Most often in Zambia in the 1980s the car hijackers did shoot. They had nothing to lose. If anyone used a gun in the course of a robbery, it was a hanging offence. And hanged they were. Absurdly enough, the hangman in Zambia was called White, as I recall it. Anyway, it was usual practice for the hijackers to shoot. I remember the cold terror, as if somebody was slowly filling my veins with liquid ice. I was sure that I was about to die, and that I didn't want to die in this stupid, barbaric way. Then the revolver was taken away, I was kicked to the ground, and as the car drove off with a racing start it came to me that I was still alive.

The third moment was the worst. It might seem exotic, almost comical, but it was the most dangerous thing to have happened to me in my life. (Nobody knows, of course, how close one might have been to a plane crash or a road accident.)

It was on one of the little tributaries of the River Kabompo in Zambia, still in the 1980s. There were several of us on a fishing trip. We cruised up the river, switched off the engine and started fishing as we drifted. We knew that there was a colony of hippos just past a point where the river split into two branches, some way downstream in the direction we were drifting towards. In good time before we reached there, we would start the engine again and turn off along the other branch. Hippos are extremely dangerous if they think their calves are under threat. And these hippos had young. Some distance before we reached the colony, one of us pulled at the cord to start the outboard motor. Nothing happened. At first there was no panic. The man in the stern kept pulling, adjusted the choke, tried again. No ignition. By now we could see the heads of the hippos. We didn't need to say anything, but we all knew that if the engine didn't start, we wouldn't stand a chance. The hippos would attack the boat, overturn it and then hack us to pieces with their enormous jaws. There would be no point in diving into the river and swimming for it. Not one of us would reach the bank – the river was teeming with crocodiles.