My whole world shrank down to the few metres lit up by my headtorch as I crested the Catogne pass and left Switzerland behind to plunge through the forest into France. The mighty Mont Blanc massif whose spectacular vistas had energised me since leaving Italy that morning had blended into the night and I felt cocooned – conscious of nothing apart from the rhythm of my breathing, the sound of my shoes on the trail and the tic-tic-scrape of walking poles …

Oh, and the Alien creature looming out of the darkness – after 14 hours and 50 miles I guess it's no surprise that twisted tree trunks took on new forms and echoes became phantom runners as I started to slightly lose my grip on reality.

I had worried about the night section before the race, scared I wouldn't be able to tag on to the safety of a convoy of fellow runners. In the end I sought out solitary moments – a lone beam of light in the darkness, only able to imagine the Alpine giants towering above me.

A hair-raising 60-minute drop through the trees brought me to the Vallorcine aid station in the valley 770m below – where dancing green lasers and thumping eurotrash beats replaced the silence. Two bowls of noodle soup, some strong black coffee and a few slices of saucisson later and it was back out into the blackness – just another hilly half-marathon between me and the finish line.

The North Face CCC 100km ultramarathon had started at 9am that morning in the Italian town of Courmayeur, where 1,950 pumped up runners waved their hands in the air to the stirring sounds of Vangelis's Conquest of Paradise.

100km Ultra-Trail du Mont Blanc CCC ultramarathon – a rare chance to practise downhill running. Photograph: Pascal Tournaire/The North Face

I took it easy on the first climbs – a lung-busting 1,365m to the top of the Tete de la Tronche pass, followed by more than 815m down to Arnuva and a brutally steep 770m ascent of the Grand Col Ferret at 2,537m. I had only been in the Alps for a day and had no chance to acclimatise to altitude – and when the distant bird call I first identified as an alpine chough turned out to be the gurgling sound of my own breathing, I slowed further – crossing the first pass in around 500th place.

Saving myself at the start meant I had energy to run the flattish section through pristine Swiss villages into Champex-Lac by late afternoon – although I forgot about my plan to fill up on pasta at this point and paid for it not long after when I found myself walking along the lakeside, unable to force myself into a jog until a gentle downhill a few miles later.

Check out that well-earned view. Photograph: Pascal Tournaire/The North Face

I spoke to double Western States winner Tim Olson before the race (he came fourth in the 100-mile The North Face UTMB the next day) and he said he tries to imagine himself "kissing the ground" with his feet as he descends steep slopes. My downhill style is a bit heavier – and it was frustrating to lose hard-won places to runners who were better able to work with gravity.

Nevertheless, by the third pass I had moved up to 250th – and overtaking people during the last half of a race is always more enjoyable than going out too strongly and losing places later on. (Thanks again go to ultrarunner and coach Rory Coleman for the tailored schedule and low-carb, diet which saw me lose weight and gain strength in the run-up to the CCC – I don't plan to go back to eating pasta, potatoes, rice and bread outside of race week any time soon.)

Nick managed to contract 'walking-pole' elbow. Photograph: Pascal Tournaire/The North Face

In the early hours of the morning, near the bottom of the final 870m climb to Tete aux Vents, I finally entered "the zone" – existing only in the present, my mind empty, a relentless running machine effortlessly eating up the trail … Unfortunately, no sooner had I become conscious of this thought than the pain in my achilles tendon screamed its return, my poor feet ached and I got my first case of walking-pole elbow – but somehow it still seemed easier to climb ever-upward than to stop.

Another brief moment of bliss followed when I realised the line of headtorches I could see stretching impossibly high above me were actually stars – though the joy ebbed by the time I eventually topped out an hour later to see the bright lights of Chamonix below for the first time since we left at 6am the previous morning to catch coaches through the Mont Blanc tunnel to the start.

A final, fast, steep 1,095m descent spat me out in the back streets of Chamonix and I crossed the line at 3.40am, some 18 hours and 40 minutes after I started.

When I spotted the CCC a couple of years ago I really hoped just to finish and mix it up with some serious mountain runners without looking silly – so to cross the line in 177th and squeeze into the top 10% was more than I had hoped for given my woeful level of fitness not that long ago. All in all, the four events of the Ultra Trail du Mont Blanc week (the UTMB, CCC, TDS, PTL – to become five next year with a new 50km run starting in Switzerland) make up an epic series of races, with mind-blowing scenery and a real carnival atmosphere.

The only downside is the usual feeling of anticlimax after a big race. But the CCC finish provided the final three points I needed to qualify for the full UTMB next year – and the sub-19 hours means I can take my place in the ballot for the Western States 100, although I've still only got a one-in-10 chance of getting in.

Before that, though, there's just the small matter of 270 miles up the backbone of Britain in The Spine Race …