It's an interesting question. I think problems will spring more from what we sleep on than in what position we sleep. You may be curled up in a ball but you're not being defeated by gravity as you would be slouched in a chair.
Actually I believe we sleep better when we're in close proximity to familiar, trusted people. I think that since we don't function so well in the dark, we've evolved to be afraid of the dark; nervous, easily startled, prone to troubling thoughts. The presence of family, friends and loved ones can be very soothing. When I sleep with my S.O. I can sleep straight through the night, but when I sleep alone I usually wake up once or twice.