Funny feeling in arm after "exercising" the whole day?

I notice that after a long day of doing some strenuous activity (canoeing, shoveling), I would wake up in the middle of the night with this very funny feeling in my arm that feels even stranger when I stretch them. Its not a prickly sensation, but more of annoying ticklish feeling. What exactly is this (just curious)? Don't know if this is important, but after these activities, I usually don't sleep on a bed, but on a concrete floor or on the ground (sleeping bag). On one occasion, I was sleeping in a cramped position.