It seems that !shop offers a perk that it's HHH Battle to the death. It seems that if someone heals you while HHH battle is enabled, after the battle time, that player will begin to receive overheal without the need of a medic. The overheal lasts indefinitely and unless the player that healed him before the hhh battle began heals him, the overheal will last. It heals when wielding weapons like Escape Plan/Equalizer and even when cloaked.