Dom Joly: The secret of happy memories? Don't keep a diary

I am desperately trying to get fit in time for my final monster-hunting trip in Nepal. I'm off to try and find the Yeti, or the "Appalling Snowman" as my son calls him. Unfortunately, I broke four metatarsals in my left foot while on a television show in Argentina and, a year later, the foot is still giving me huge problems. This is very unfortunate as I have a six-day trek ahead of me. The word "trek' is a very passive sounding description for clambering up huge mountains at very high altitude while very cold in order to look for a hairy missing link.

I have to admit that I'm not that keen on walking up mountains; it's not my idea of fun. I like flatlands and cable cars. An option that is sadly not available in the Himalayas.

I filmed a show for Channel 5 about five years ago (they still haven't shown it – they must have a huge surplus of quality stuff to broadcast) in which I went to Nicaragua and climbed up a volcano. I can't remember why the volcano had to be climbed or why Channel 5 wanted to film it. "Because it was there" is the usual answer but, whatever, it was sheer torture and that only lasted one day, not six.

One of the joys of writing a book as opposed to making television is that I can control how much the reader knows of my travails. I can turn despair and pain into bravery and humour and nobody is any the wiser. Whereas on television my every moan and groan, my every wheeze and whinge is lovingly covered by voracious, sadistic camerapeople. There's nothing telly likes better than a podgy minor celeb puking his guts out from over-exertion or weeping frantically into the humid lens on the cusp of a total panic attack.

The human brain, however, has a wonderful way of wiping clean memories of such trauma, and only retaining positive highlights. So, if I think back to my volcano-climbing day in Nicaragua, I remember getting up before dawn and trudging off into a misty forest. I remember sitting on a log half-way up and gazing down over Lake Nicaragua. Then I remember reaching the top and swimming in the lake that filled the summit crater and coming across some very peculiar fish. It is quite a fond memory. Unfortunately I also have a DVD of the finished show (still unaired on Channel 5 ... did I mention that?) in which I appear to be very near death. I weep on several occasions and I frequently enquire as to the possibilities of turning back and whether the Nicaraguan emergency services possess helicopters.

I love how my memory does this to me. I'm starting to realise that this is why I travel so much. However hideous the trip, give me three weeks and I'll remember it as a glorious adventure. I'm already starting to think that my recent trip to the Congo was great fun not a hideous journey into the heart of darkness. I believe that this historical airbrushing by our brain is the only reason that anybody ever goes InterRailing. The concept is great – a couple of hundred quid and you can travel anywhere in Europe by train for a month. The reality is sleeping in boiling hot train corridors as you travel through Yugoslavia on your way to being CS-gassed by a gang of robbers before being savagely beaten up by a man in a bar in Athens. That was my reality anyway, I know this because I kept a diary. All I can remember is a girl I snogged in Munich and discovering a perfect beach on a Greek island after a two-hour Vespa ride.

Anyway, can't hang around chatting: the running machine has just hit incline 15 and I'm entering the "death zone".