I find this really hard to control! I'm so uncomfortable on my left, even if I start there I can't stay there, I always wake up on my right. Even during labour with DD my most comfy position was lying on my right. Once my waters broke the midwife hooked me up to a monitor and no way in hell would she let me go anywhere but on my left. In the end I said bugger this, rolled over and hey presto, DD got into position and pushing started!

So now I subscribe to my body knowing what it's doing, and if something was wrong it wouldn't be the most comfortable position to be in.