Five-minute memoir: Lydia Syson on developing a fear of heights

Heights never bothered me when I was little. My mother would quake and quail as I teetered on cliffs and castle battlements. I just pranced closer to the edge. That breath-catching rush on looking down was half the fun of getting high in those days.

Now I'm as bad myself. "Careful!" I call to my children. "Careful! You'll fall. Come back." And visions of small tumbling bodies somersault through my mind.

With a parent standing near, worrying for you, you can hand over the possibility of tragedy. Here, take this a moment, I don't want to carry it. Like a coat that's too hot and heavy. Fear of falling arrived in my life at the moment I realised I was alone; it came without warning, high above the rainforest in Guatemala. But I'd seen it before. I knew what to expect.

Soon after my 18th birthday, I took a trip to Moremi gorge in Botswana. I was working as a teacher in a village in the north-east of the country where I'd first learnt to read and write. One weekend, a Peace Corps friend and I hitched to the Tswapong Hills to see a colony of Cape vultures. In Palapye we picked up Pete, a British Council teacher of the bearded ectomorph variety. Tall and milky-skinned, he was a vegan who smelt of biscuits and perhaps didn't spend much time in daylight: his passion was astronomy. We stayed a night and looked through his telescope at Botswana's unimaginably clear skies.

Our guide at the gorge was Per, a Danish development volunteer of exceptional competence, based nearby. This was a magical spot, full of legend as well as wildlife. We drove off into the bush in Per's four-wheel drive, and he knew just where to stop.

Getting up to the cliff from which we could look down on the nesting vultures was a rewarding scramble. In a dry country, the thrill of water and greenery is intense. Pale, elongated tree roots fingered their way to moisture down pink granite boulders streaked with black, and made good handholds. I remember hanging plants like vines, and the sound of vulture wings above. The birds were huge, and pleasantly menacing. Their heads moved from side to side as they checked us out, reminding me of the flying monkeys in The Wizard of Oz.

Per was gentlemanly, offering hands and help to me and Catie as we clambered up, but not insulting Pete with assistance, though we wished he would. At the top, Per produced binoculars, which we shared, perching on the cliffs. He had found us a perfect view. We counted vulture chicks, and felt adventurous.

Coming down was harder, of course, though the only really tricky section came close to the end: a shuffle along a narrow ledge, with rocks above and below, and a drop into a deep and icy pool. On the return, if you were right-handed like me, you had to support yourself with the wrong side of your body, which I didn't enjoy. The third to cross, I turned to look at what I'd conquered as soon as I reached safety. And I saw that Pete was stuck. Really stuck.

I'd never before witnessed anyone frozen with terror. Crouching on hands and knees, he couldn't move at all. Not far off childhood, I found such naked fear both horrifying and transfixing. How could a grown man let this happen? I felt part of the humiliation.

Per shuffled back and tried to coax him. It was getting dark by the time we accepted it would never work. Pete had retreated to the opposite bank of the pool. He began to undress, though swimming was an equally terrible prospect. Was it the intense cold, or the depth? Or unseen threats… bilharzia, or water snakes? I can't now remember.

Elongated body rising palely from shadows, underpants loose as a loincloth, Pete stood there, an emaciated Christ-like figure. Still he couldn't move. Eventually Per stripped off, too. He brought Pete back through the water, clinging to his shoulders. We didn't talk about it around the fire we lit later. We slept out, under the stars.

Four or five years later at Tikal, a small gathering watched the sun set in silence over an endless sea of treetops at the top of a towering Mayan temple. Our backs were firmly against the wall, our feet pulled away from the edge of an unguarded ledge. But when it was my turn to step back across the gap at the corner, a rush of nausea felled me. I felt myself swaying, losing my balance. I knew nobody in this country. There'd be only a camera and a room key to identify my corpse. I had to get myself onto a vertical iron ladder to descend.

Strangers were kind to me. I thought of Pete and I forced myself to move.

'A World Between Us' (Hot Key Books) by Lydia Syson is available in paperbook, ebook and as a Multi Touch edition for the iPad