[Desuma Malevois]

At this point in time you should have at least one regeneration item, and probably more. If you're like me, you memorize very few healing spells, preferring to depend upon the items instead. So yes, I would think the "rest until healed" option is the problem. The last time I was in the Underdark, I cleared out the beholder city in only a few hours. It shouldn't take long with the right items.