Aren't hammock's real bad for your back over longer periods of time? This is just something I've heard and not researched but I had the impression you needed your back mostly "straight" when sleeping.
They're pretty popular in South America... I've got Northern European ancestry but no back problems, and I sleep well. You can actually get pretty straight in a hammock, I think a lot of people overestimate the curvature. I think this blog has some good pictures to show what it's like: http://www.treklightgear.com/treklife/hammock-angle/