Don't be scared! That could bring on anxiety and be a self-fulfilling prophecy. If you're a fan of Dune, I suggest the litany against fear.
“I must not fear. Fear is the mind-killer. Fear is the little-death that brings total obliteration. I will face my fear..." - Frank Herbert, Dune
If you can handle the bag, the j-pouch will be no problem. There will be a getting used to it period. . .for both you and your body. You'll definitely be able to get 8 hours of sleep. Perhaps not at first, but you'll get there.
Good luck!