Starting a few years ago, I ran into an oddity while out hiking, where I get a tingling/numbing sensation in my fingers (to start) but soon escalates to include the whole arm, face, sometimes chest. Not a lot different from the sensation of certain drugs (N2O comes to mind).
It doesn't happen all the time (maybe three times a year), mind you, and doesn't seem to be dangerous (no loss of coordination, consciousness, or anything like that) and it goes away within about 5 minutes if I stop. There are certain conditions that also seem to apply:
* Only happens when going downhill. If I start up a hill again it goes away within minutes
* Only happens at lower altitudes, usually less than 6,000ft
* It also only seems to happen after I've been out hiking for 3-4 days.
It doesn't seem related to the long-distance nature of some of my hikes, as it can happen on shorter outings of 7hrs or less.
I described it to a few other partners in crime, but none of them reported anything similar. It puzzled me for the last few years and I only recently determined the cause. I'm curious if anyone else has run across this or what one of our medical practitioners might make of it. I'll reveal the cause later - it may surprise you. Or may not.