I know what you are talking about because I sleep in a fairly similar position, but slightly more comfortable. Instead of being straight on my stomach so that I have to have my neck bent, I sleep on my side and then pull my top leg over and forward so that it tilts me downward, and have my hand under my pillow to support my head. Anyway I get SP a lot because of this, and pretty good LDs too I might add. I don't know whether to attribute it to the position though.