Gideon's rule of "3 or more"; as others have said, check angle and do the finger test. Lying in the hammock reach up and try to "bend" the ridgeline. You should be able to bend it but if its super tight and you can barely bend it up, then the angle on your suspension is too shallow. Next, is it an adjustable ridgeline or fixed; if it's fixed no worries. Hammock width "and" length; an extra few inches in width or length can make a more significant difference than you might think. Finally, some hammocks just don't feel as good as others even when all other things are equal. Finally, you do have to get used to it. I sleep on my side in a bed so when I head to the woods and sleep in a hammock it's different and not everyone has a heavenly, miraculous sleep in a hammock! On my worst nights it's still better than being in a tent, on the ground, on a pad. I think the single bigest factor is the angle of your hammock suspension. Good luck figuring it all out!

Gideon