Yeah - i can be totally relaxed but not sleeping for a long time on my back, but to fall asleep i usually have to turn over on my side and curl inward or at least partially face down. I've thought about that - probly protecting the privates area - making it less accessible.
"That you are here - that life exists, and identity; that the powerful play goes on and you may contribute a verse. . . What will your verse be?" Robin Williams as John Keating in "Dead Poets Society"