I introduced a system which at it's core made natural healing towards the 'gritty' end - especially if no healing kits were available,
Nod, what folks usually mean when they say 'gritty' healing, slower rates of recovery, restrictions on spending HD, etc...
but...
but also did the same for magical healing, which requires Healing HD to be used up on a one for one basis with the level of the slot used to fuel the healing spell...
... the healing HD of the target are used first, and if there are none of those left, the Cleric or Druid etc. can burn their own HD to fuel the healing spell.
It works wonderfully well, and means magical healing is draining and costly.
I'd often thought of healing spells using the target's HD size instead of their usual dice, or allowing HD to be spent on top of the healing effect without the short rest, but I never thought of pegging HD to slot level to fuel the spell, making healing 'above & beyond' compared to other spells.
I love the caster spending his own life force to fuel the healing when the subject is out of his own, too. As comparatively rare as instant healing is in S&S, where it does occur, that's the kind of 'high price of magic' you'd expect.
Is that all yours or did something inspire it?