The closest I get is the "release" or "drop" or similarly hard to describe thing that I could do when trapped on a hot bus on hot days that allowed me to handle the heat, but it only worked every so often.

I imagine I was triggering a change in blood pressure through conscious vascular relaxation or similar. Or maybe I was just fooling myself. But it gave a few moments of reprieve from the oppressive heat and allowed a reset before I started boiling again. (Getting off the bus would have meant being out, walking, in cooler air, but under the hot sun for even longer.)

We don't get hot weather a lot in the UK (even if it is increasing in frequency) and even more rarely have I found myself on a bus during the brunt of it, so it's not exactly something I have much need or opportunity to practise.

I wouldn't be surprised if it's some kind of control over the "blood runs cold" fear response. That would fit with my psychology, tbh.