Superman didn't start healing this fast until something started to happen. That being said, Doomsday is just the first part of this mission. There are two more objectives you will have to deal with.

Now I didn't tell you guys to stop messing with Dimensions cause your beating doomsday to easily, thats fine. I'm telling you cause when you all start messing with dimensions like this, you might create a tear and summon Trigon or something. Trigon makes doomsday look like a weakling.