It's Sunday morning and I'm standing in a park gazing at a sea of red and white. Hundreds, nay thousands, are dashing around all dressed as Santa - and I'm one of them.
Have I gone mad? You may think that from my straggly white beard and ill-fitting jacket. Two Santas even grabbed me to pose for a photo with a tourist-like awe - telling me it was because I stuck out as a tall Santa (at 6ft 5). Also, my beard kept flapping into my face.
It isn't a quarter-life crisis, I was part of this Christmas cohort in Victoria Park, east London, for a five kilometre charity run, having chosen to do it for the National Literacy Trust.
I'm hardly the most experienced runner. My regime is the same as Usain Bolt, except I remember to eat the chicken nuggets and don't get around enough to actually practising my run. For me, this was my London Marathon. I was fueled by a desire to get to the pub sharpish for a Sunday roast.
By contrast, my two co-runners (co-Santi?) rivaled gazelles in their athleticism. One of them had agreed to do this on her 25th birthday, who I'm calling birthday Santa. The other, who I'm calling Jock Santa, just wanted to win.
Before I could regret my foolhardy decision to join, a chirpy Santa hopped onto a raised platform to act as master of ceremonies.
"Time to warm up!" MC Santa told the hordes. With zombie-like groans, the Santae amassed and we went through star jumps, squats and skipping. We finally were released and, as if some signal had been sent out, the Santas charged onto the starting line to take positions. It was on.
Once the starting whistle went, I broke off into a run as my beard flapped away. Trying to avoid inhaling a ball of beard, I powered on through Victoria Park's twists and turns. Jock Santa, meanwhile, had dashed off through the crowds to fight his way to the front.
Some male Santas had broken off after the first kilometre for a bit of momentary relief against any nearby wall. Others were starting to throw off their beards, hats and Christmas togs to try and run quicker. One shameless Santa provoked howls of outrage by zooming on by on a scooter, rather than his own two feet.
I fought to keep my place in the Santa stampede as many tried to overtake. Plodding along, I kept my position as a increasingly sweaty Santa.
Looking out at yellow signs to count off every kilometre, my spirit soared as I saw the final number - '4' - showing I was on the final stretch. Yes, the finishing line was within my sight.
But just a few metres away, even my fellow runner Birthday Santa couldn't resist trying to break off to dash over the finishing line first.
The vicious contest of Christmas athleticism finally came to an end as I beat hundreds of other Santas to the finish line. Then again, many of them were going for a second tour in a 10k run.
At least I found out I can pull off the Santa look and run five kilometres at a not-too tortoise-like pace - and my Santa silliness will help someone this Christmas.
You can still sponsor my Christmas Santa run at: http://www.justgiving.com/AsaSanta