I've read the thread about why its not good to sleep on your back, but can anyone tell me why its not good sleeping on your stomach - or is it just that as you get bigger you end up rolling all over the place like an out of control beach ball??

I've always slept sort of half on my side and half on my stomach with one knee drawn up almost to my waist (I'm sure that's perfectly clear for everybody ) but now I'm finding that gravity is taking over a bit and I'm ending up more and more on my stomach.

Is it something I should be worried about and really try hard to avoid, or is it not that bad? Lying just on my side is giving me very sore knees!!