It’s day three in Colca Canyon and we are told that we have to leave at 3am for the last ascent. After the two cases of altitude sickness and one case of collapse from exhaustion in our group the day before the guide advises us that we should get mules. We decide to get one for our bags and another to share between the group when things get too much.

Ingrid and I have just about recovered from the day before's trek, but every one of my toes has a huge blister on it. I curse my boots - they are proper hiking boots and cost me a fortune. Why am I in so much pain? Boosted from my Hurculean efforts the day before, I decide that no matter what, I'm going to finish this treck on foot - after all it's freezing, so at least we won't have to cope with the heat like yesterday.

We set off. It takes about ½ hour to reach the man with the mules, so despite the cold the layers start to come off. When we arrived at the meeting point the guide asks who wants to get on the mule first. Before us is a jagged wall of rock rising steeply into the night. Nobody comes forward, the guide signals to me, so I offer myself. Forgetting to put my layers back on, I scramble on to the animal’s back and he shoots off leaving the group behind.

I realise very quickly that he's not going to stop to wait for the others. The second mule with the mule owner and the bags is way behind us. Tim is desperately trying to keep up with me to the point that he is almost running and I am already starting to have what feels like a minor heart attack. Eventually Tim has to give up and I am left on my own.

So what's the big deal? I have never been so frightened in my whole life as I was that night - real fear - fear like I have never experienced before and hope I never will again.

The track was narrow and really steep. It was also covered in loose rocks. In order to climb the mule would position its front hooves at the top of a rock, pause a second and then swing his back legs up while at the same time jutting forward with his front hooves. This meant that I got a good view over the edge of the cliff every time he did it.

His hooves were no more than 10cms away from the edge – or at least that’s what it looked like from my position. It's not that I mistrusted the mule. I knew there was virtually no chance at all that he would loose his footing. The fear was that I would fall off and go hurling over the cliff. Every time he kicked his back hooves I slid down his back.

Pitch black and starting to freeze. Why the hell will this animal not stop? We're supposed to be taking it in turns. He stops. Oh thank God! I can hear the faint tingling of the mule owners radio in the distance. I'm using the mule for warmth. I'll just sit tight and wait for him to get here and then Ingrid can take over. She must be exhausted by now.

The tinkling gets slightly louder, then a whistle, then silence.

I call out 'Senor? Senor?' Nothing. I start to get really paranoid now. My stupid, infantile fear of the dark. Why isn't he answering me? Why can't I hear his radio anymore? How far back are the others? What were the guides talking about before they asked me to get on? Why has this animal not stopped?

I go to get off the mule. He instantly starts to move again. Clearly he had no intention of waiting for the others. He was waiting for the sound of the radio which I can now hear tinkling in the distance again. I call out to the guy telling him I want to get off in the best Spanish I can muster as loud as I can. I can hear my voice echoing down the canyon. Nothing. Just the faint tinkle of a radio. Why won't they let me off?

Onwards and upwards. We passed a cross on the way which marked the spot where someone had fallen off his horse. I remembered our guide had told us about it on the way down. Three people have fallen to their deaths in the past.

It was at this point that I did two things - pictured the faces of all my family and friends one after the other and resigned myself to the fact that I actually might die alone on the mountain.

I know this sounds crazy, but it's true. I was constantly trying to get the animal to stop and it just ignored me. Every time I slipped back a dark thought teased me with the fear that I wouldn't be so lucky next time - there we times when we were practically vertical.

I could hear a very slight tinkle of the radio. I knew he was behind me, but couldn’t work out how far. I was desperate to get off and concerned for the others – how were they faring? Can’t think about that now. I just have to keep hold of the rope and stop myself sliding. I'm just going to have to go it alone.

I suddenly find myself amazed at how calm I am. Although my breathing was close to hyper ventilating at first and I was wincing with every step up, I've finally settled and am just praying that the trek will be over quickly.

It has started to get light and I can now see the moon which is lighting the way. It occurs to me that if I do fall, Tim is just below somewhere and would very likely see me go off the edge. I am not going to fall. I know how to ride a horse and I am not going to fall. Stop being so ****ing stupid, hold on tight and take in this amazing view that is being given to you. If only I could let go of this animal and touch those stars. If only I could let go of this animal and get to my jumper. Why didn't I grab it when we stopped? It’s in a bag, on a hook in front of me, but there is no way I can reach it with one hand, and there is no way I’m letting go of the reins and the saddle. I’d rather freeze than fall.

After about an hour my fear subsided completely. I found myself moving with the mule and my confidence grew. He had expertly jumped so many rocks and corners and I had managed to stay on each time. I even managed to look down a few times as we swung up another rock. Enjoy it Dana, enjoy it.

That's when I realised just how cold I was. I was shaking, my ears were burning and my head pounding. I'd been cold all along, but I was clearly so concerned with being terrified that I didn't realise quite how cold. There was no stopping the mule and you could not let go of him for obvious reasons. I had taken my big jumper off and left my hat in my bag because the initial ascent we had to do to reach the mules was so exhausting. There was nothing I could do about it. My jacket was round my waist and I couldn't get to that either.

I decided to focus on the amazing sky which had started to get lighter and a fantastically bright crescent moon that looked like I could touch it if I only dared let go of the reins. I continued like this for another hour and a half, singing to myself, grabbing whatever warmth I could from the mule's body. I was now totally calm and apart from the cold, enjoying the ride. I wondered how the others were doing. Surely Ingrid had collapsed by now. Why the hell was the mule ordered to just go straight up? We were supposed to be sharing it!

Part of me is really disappointed. We purposely didn’t get a mule each because we wanted to attempt to do the rest of the canyon on foot, but I dare not attempt to get off this animal. And anyway, I’m on my own and it’s bloody dark. I think I can still hear the tinkling of the radio, but it’s far away.

After at least three false home runs we finally reached the top. I kept thinking 'this must be the top' and then we'd get to another steep bend and another sheer ascent. When the animal finally stopped on the wide, flat road at the top I jumped off and I kissed that mule.

I stood there, shivering, watching the sun rise until the mule with the bags and the mule owner arrived about half an hour later. We unloaded the bags in silence. I wanted to scream at him, tell him what he'd put me through, but what was the point? Clearly the guide had mis-informed him. Even if he hadn't, what use would shouting at him be now? Without saying a word to me, he and the two mules went back to fetch the others.

I was finally able to get to my layers. My hands were frozen underneath my gloves and my ears were hurting, but at least I had more than a Tshirt on now. What a bloody idiot I am. Although they could have warned me the animal wasn’t going to stop.

I waited for nearly two hours at the top for the others. I tried my best to chill and just enjoy the sunrise, but I was worried for Ingrid and for the other girl in our group. She had collapsed the night before.

My lips had turned completely blue and were totally cracked and shrivelled. My hands were cracked and bleeding slightly and even though I put on every layer I had it was only 6 hours later in the blistering heat that I managed to stop feeling cold and start to peel them off.

The worst thing about this whole experience was that I never got to walk the canyon. When the others arrived the couple who had been annoying everyone for the whole three days started shouting at me saying I had purposely taken the mule for myself. His wife had my mule for the last part of the trip. My heart leapt with joy as I saw her come up the last ridge. Finally, they were back. Then I realised she was sobbing. I never found out whether it was because of exhaustion or the sheer terror of riding the mule. They both looked exhausted, and to be honest, there was a little part of me that was satisfied. Not because of any of the days before, but because I was clearly in a very bad state when they found me and they didn't care - they just instantly assumed I was the bad guy.

Ingrid realised straight away. It was Ingrid I was really concerned about, but she seemed quite elated – from the joy of achieving the trek. Tim didn’t stick up for me or seem too concerned about the experience at all. I think he was just glad it was over. He made fun of me for days, calling me a cheat because he walked the hardest part of the canyon and I took a mule. He has no idea.