Assume you're making a turn-based RPG.
Every time you revive, 10% of your maximum HP is knocked off.
This is persistent after the battle and can only be recovered at inns. I'm referring to in-town inns, since there's a doctor available there.
If you have character classes, you could have a "doctor" class which can heal injury from a tent.
Of course, there's a lower limit which cuts off at say... 50% of max HP.
Come to think of it, that's rather harsh. In addition to this, all overkill when the character is at two HP or more does not KO but instead drops HP to one, giving you a chance to heal.