I'm 31 weeks along. I still occasionally sleep on my back. Funny, because I'm usually a side sleeper. When I wake up and find myself on my back, I try to see if I feel dizzy or funny. Nope. Baby seems fine, too -- he's kicking and rolling either way.

I suppose if my vena cana was really being squeezed, I would not be comfortable! I do go to sleep on my side though, so it's not like I'm intentionally sleeping on my back... I'll ask my doc next time I go in for a check up but I feel it's one of those "you'd know it if there was something wrong" things.