I defeated an advanced demon scout and my HP's went from 1299 to 1029 (this is normal), I caried on and after defeating a few zombie archiologist in quick fights (no xp) I noticed my HP's had risen to 1320 ( the level I can top up to with potions).
I never enterd any other screens only movement and fights.
Sorry I don't have the full details, I can wander the desert with impunity (except those dam ants!) so I don't check my HP's often when I'm working on my scorpion quest.