Vampiric Sacrifice

Subtract from your own health in order to give half of the subtracted health to an ally. You may subtract up to fifty HP every turn, and may distribute it as you see fit among allies. If the spell is still active at the beginning of your next turn, you MUST subtract equal to or more than you took the turn before.

You may subtract health even while you are unconscious if someone else activates the spell for you (i.e. via campaign-specific things such as a magical ship), but this does risk death if you pull too much.