So i was in inferno difficulty act 1, in the den of the fallen level 2. My hp droped to 2k during the combat, and it simply got stuck there. I couldn't fix it by drinking potions, using preparation, or even with the guy that heals you back at tristam. The red thingie was what made it really annoying. It simply remained that way until i decided to go outside and get hit. Once i did, my health got back to what it actually was.