I've only played Morrowind for a short time right before Oblivion came out, but already I still think Skyrim should have the rest/sleep option even if there are prowling enemies around and I think it's realistic being attacked while sleeping. I mean, how the hell would my character be a psychic and go, "Hah! I think there's someone nearby. I better not rest, dammit." I would crouch low and the eye detection would pop up, warning my character that there's someone nearby even if he didn't see them.