I mostly sleep on my stomach but sometimes on my side. I don't know bout the neck, but if you have backaches you're not supposed to sleep too much on your back. My mom has a bad back and her chiropractor told her to sleep on her stomach as much as she could because sleeping on her back puts alot of pressure on it and sleeping on her side puts the spine in a curved position. So I guess it doesn't matter how you sleep cause no position is good for you lol