Originally Posted by dla
I sleep with knees slightly bent usually.
This pain you mentioned is what confused me when I searched. It wasn't clear whether people were hyper-extending lying on their backs, or on their sides. As I understand it, the diagonal should be pretty flat.
I'm sure this would all make sense to me if I tried a hammock out.
You can have problems with the knees sleeping on your back or on your side. . . Either way, the knee can be pulled in a direction that it's not meant to go. A diagonal lay will get you pretty flat, but not necessarily perfectly flat.
As has been said by you and others, the best way to learn is to try it out and see. You can get a decent hammock for 20 bucks or so to start off with, or you can try to make it to a group outing and get a chance to see and try a lot of options before you buy.