Eternity

Whenever you drop to 0 HP you instead role 3d10 and gain that amount of HP. All damage after falling to zero is nullified. The spell does not activate if the target dies in a way that would destroy the body or sever the soul from its host. After the spell is casted on a creature it can't be used on them again for 24 hours. 

When casted at a higher level gain 1d10 per spell level.