Extremities need their sleep too!

Or at least it seems that way a lot of the time! When I lie on my bed or on the couch playing iPod Touch games, when I sit at my computer doing whatever it is I happen to be doing at the time, when I sit on the floor playing board games (or reading a book, or eating etc.), my limbs often fall asleep. I wonder if there is any particular reason this happens so often for me or if this is just average amount of limbs sleeping?

It's just an idle thought, I suppose, but it's one that puzzles me as I sit here, my right leg deciding that sleep is what it should be doing.