The wounds you receive in Divine Divinity are not medeocre. A slash from an axe will not heal without medical attention. Survivor's Instinct is the knowledge to treat your wounds to help them heal. Consider having zero levels of this skill meaning that you can bandage a would, but with all the movement you make, it doesn't get a chance to heal. With rest, you can let the wound heal. If you do not sleep from day to day, you won't heal naturally because the body cannot handle that kind of exhertion.

Perhaps Survivor's Instinct and sleep need to be ammended:
Level 0: Restore 25% health when you sleep.
Level 1: Restore 1 hit point every 12 seconds. Restore 40% health when you sleep.
Level 2: Restore 1 hit point every 10 seconds. Restore 55% health when you sleep.
Level 3: Restore 1 hit point every 8 seconds. Restore 70% health when you sleep.
Level 4: Restore 1 hit point every 6 seconds. Restore 85% health when you sleep.
Level 5: Restore 1 hit point every 4 seconds. Restore 100% health when you sleep.

Also, if they make potions harder to come by, this will make this skill or Alchemy a lot more useful. I annoyed that my character has more health potions than he can carry, all found or purchased.