Well- I'm pretty sure the egg won't get squished by sleeping on your stomach- it's pretty well protected in there.But after BDing you should lay on your back and elevated for at least a 1/2 hour(I think that's how long). But if you happen to have a tilted uterus then it's better to BD with you laying on your stomach and DH from behind. Other than that I don't think it really matters how you sleep.