In recent years when I'm running or mountain hiking, sometimes my left arm
will get the sensation of "going asleep" (as if from lack of circulation).
Sometimes after the exercise the left arm will also be slightly "palsied"
(slightly unresponsive and shaky).

I haven't heard of this happening in other people and I'm wondering what's
going on. I'm in my late 50's, and have been exercising all my adult life.

Thanks for any informed responses.