for me it's always the right side, curled up, sometimes with one leg straightened out. I can't really sleep on my left side- it puts painful pressure on my colon, plus it makes me have to pass gas- which isn't always just gas! Every now & then I go onto my back, but it's the right side 90% of the time. Once in a while I'll lay on my stomach for a bit, but I never fall asleep that way. Oddly enough that position doesn't bother me much at all, just the left side is uncomfortable.