The obvious life changer is the most elusive – that moment when you surrender the cushioned, aquatic world of the womb for the rigours of air and noise. Suspended by a now useless umbilical cord from the woman you never chose but can never really escape, you change your breathing, your blood circulation, even your blood itself. Yet no one remembers it. In my case the breathing change didn't go so well – I'm incorrigibly lazy – and the midwife had to administer a touch of medicinal brandy and thus give me something to live for. So the story goes.

But is an unremembered moment a real experience? Perhaps not. So I'll take another umbilical cord, one that also maintained my life in dramatic and more memorable circumstances: the rope that saved me on the day in 1975 when I fell off a mountain. Up to that time I'd been living a life strung between two poles – literal or metaphorical, take your pick.

One pole was the hedonistic world of the Mediterranean, always a draw to the budding writer and particularly to one who, with an adolescent's taste for purple prose, had been swept away by Laurence Durrell's Alexandria Quartet. The other pole was the mountains. I'd fallen in love with the mountains in the way that an adolescent may fall in love with a beautiful, difficult, complex and totally unsuitable older woman. I'd struggled to be worthy of her, I'd striven to keep her happy. But still she remained elusive, bestowing her gifts only occasionally and with the disdain that a suitor like me deserved. Finally, she rejected me.

It was a strange, arcane world, that of the climbing fraternity. We spoke a language that outsiders couldn't comprehend, planned adventures in damp and foetid pubs, drove miles through the night to gain remote crags as the sun came up. A granite-face Scot by the name of MacInnes had invented an ice hammer with a steeply angled pick with which we clawed our way up vertical ice while perched on front point crampons. This instrument was a totem, a symbol of the strange rites of our religion. I'm mixing metaphors, but climbing is like that, an overcharged pursuit that engenders florid language and obsessive behaviour. One winter I even left a beautiful girl called Sally on her own in London to make my way to Scotland because the ice routes were possibly, just possibly, coming into condition. I must have been mad.

On the other hand, and apart from all this, I'd also fallen in love with the Mediterranean, those sights and sounds, those scents and tastes that have haunted the English mind ever since the days of the Grand Tour. Smells, bells, yells. But also sun and sea, the tortuous knots of olive tree and vine, the shadows of monsters such as the chimera and the gorgon.

My parents were living there, in what was to be my father's last posting in the RAF. It was a glorious end-of-empire existence in a house on a hill with a dozen servants and a terrace where one could look out across half the island as though one owned it. The contrast with the Scottish mountains could not have been greater. And there was also another woman in the mix, a Calypso, dark and Latin to Sally's Anglo-Saxon blonde.

Embedded within this curious dual existence lay another dilemma: in the Mediterranean, I wrote. In Scotland, I climbed. And the one seemed to exclude the other. Which, I wondered as I oscillated between these contrasting states of luxury and austerity, would be my future?

Given such tensions, an explosive resolution was perhaps inevitable. It came one Sunday in January, a day when the sun, for a moment, pulled apart the grey rags of Scottish cloud and revealed the North Face of Ben Nevis in all its winter glory: an Alpine landscape of iron-grey rock pillars interlaced with snow and ice. A friend suggested we try the newly climbed Hadrian's Wall on the flank of Observatory Buttress, a 1,000ft climb that starts with 200ft of almost vertical ice, pauses at a snowfield, breaches a band of rock through a dreadful ice chimney, and concludes with 400ft of steep snowfield. It seemed a good idea at the time, but halfway up this route, with all of the technical difficulties overcome and only the steep snow slopes to climb, I was avalanched. Throughout the day we'd been climbing through small cascades of spindrift. If you're not cold and not frightened and if the sun is shining, spindrift can be very pretty. It hisses and sparkles, a rivulet of diamonds catching the sunlight and throwing it about the place with gay abandon. But this time, perched on crampon front points and the blades of two of those MacInnes ice hammers and with half the climb below me, I met my nemesis: one of those streams of snow crystals rose in intensity in a way that none of the others had. It was like being engulfed in an ocean breaker, but a wave of snow rather than water. The sky above me went dark. The cascade overwhelmed me. I fell, flew, went over backwards, over the rock band I had just climbed, down the short snowfield and over the cliff below.

Falling is easy. Time slows. Each foot of the fall is delineated in your mind as though it lasted a minute, and yet for the duration all fear is cancelled and you simply wait to see what will happen. What did happen was that I came to a halt hanging upside down on the face of a blank, icy cliff. Somehow the rope had held me. I was out of sight and more or less out of sound of my climbing partner up high above, but I was alive. I righted myself and cut a foot-sized ledge in the ice of the cliff. Cloud had come down over the mountain and I could only glimpse the snow slopes below through breaks in the vapour. Black rock precipices, draped with snow and ice, were all around me.

I contemplated my existence and in the ensuing 22 hours while we waited for a rescue I made my choice. It was not a courageous choice, but at least it was an admission of what I had always previously denied: my courtship of the mountains was absurd. I was too feeble a suitor for such an enterprise.

Anything in a novelist's life is grist to the mill of his or her craft and eventually I used my experience of the mountains in a novel entitled, obviously enough, The Fall. I might have been a poor climber, but I was convincing enough when writing about it: the book won the Boardman Tasker Prize for mountain literature, a prize awarded under the auspices of the Alpine Club. However, all that lay over two decades in the future.

For the moment I was nothing more than a survivor, uncomfortable to find myself on the front page of the national dailies. That is how Calypso, far away in her Mediterranean island, got to know of my plight. The day after I got off the mountain I wrote her a letter explaining my feelings about her and about my future. I told her I was abandoning this absurd pursuit. I wrote other things as well, but I can't recall them now and she has never let me see the letter. Within a few weeks I was preparing to leave the country. I didn't have much to take with me – just clothes and a hi-fi set and my now useless climbing gear (I have it all, to this day) – but I did carry with me a renewed desire to get on with my writing. And I wasn't sorry to leave Britain behind: the country was a sour, grey place at the time, in the midst of industrial dispute and political unrest. The brilliant Mediterranean seemed altogether more promising. I've never really left it.

Simon Mawer was born in 1948 and now lives in Rome. His latest novel, The Glass Room (Little, Brown, £16.99) was nominated for the Booker Prize in 2009