Discussion: Careful now

This reads exactly like accounts of how people start chronic fatigue type problems. I had a similar experience during the 2016 London marathon from which I’ve never recovered.

Have a bath, a big roast dinner and some sleep with no alarm?

Could be low-level hypothermia as well

I'd guess you're not fully over the cold.
Carrying a virus can mean you've got lower energy reserves meaning when you race you burn through them more quickly and bang, your battery is flat, you're up a mountain and hypothermia stalks you.
Happened to me in Borrowdale a few years back. Funny thing was I had a couple of psychological hints - one of them - at Honister the thought randomly entered my head "hey, why not just run down the road from here ?" After wondering where that idea had come from I pushed on up Dale Head and about 20m past the summit cairn that switch that you mention just flipped. I stopped. From there - what should have been a 20 minute descent took me 1 hour 40. I spent a few spells lying in the bracken down amongst the mines shivering (it was 19 degrees in the valley that day). As I walked along the farm track the final few hundred metres into Rosthwaite I registered the crackle of a radio and a couple of heavily kitted out guy heading out. "Are you mountain rescue? " I asked, "yes" " you're maybe off to find me" They were. Kate had started wondering where on earth I had got to, had spoken to Scoffer and he had checked that I'd long since left Dale Head

The psychological hints are def a thing, when I used to do hard intervals on the treadmill I began to notice the flip in my inner monologue at a very specific effort level.

I would love to know if the shutdown of the body that comes from ignoring these warnings is the brain activating a survival mechanism or if it’s just catastrophic system failure.

To be honest, I notice a flip in my inner monologue after five minutes of jogging on a treadmill. Definitely a survival mechanism.

:-)