Dropping to 0HP
Dropping to 0HP is a huge deal. It means you’d be dead if you weren’t a hero. In 1st Edition AD&D if your PC dropped to 0HP, they fell into a coma for up to an hour, after which time they needed to spend a minimum of a week in bedrest. I like the dire nature and close-to-death feel that something like that gives, so here’s how we’re going to deal with near-death experiences:
Dropping to 0HP will require resting with no travel for two full days, added on to any other resting penalties that accrue. Also, the character will have five total levels of Exhaustion for those two days.
3 Successful Death Saves stabilizes a character as per the rules as they were written as does the application of magical healing effects. Also per RAW, if you roll a 20 on a Death Save, you regain 1 Hit Point and become conscious. Keep in mind that all the non-coma effects of having dropped to 0 HP (info here) will be in effect as you awaken in the middle of battle with a wound that would’ve killed a lesser person, so if you think you’ll just hop back into the fray… reconsider unless you’re a tried and true hero.
Failed Saves work as follows: Characters do not die until they fail 6 Death Saves (rather than the 3 in RAW). However, for each Failed Save, the character must be on bedrest, in civilization for a full day, bedrest, with help, in a campsite for 2 full days, or bedrest for 4 full days if there is no campsite or if being transported in a wagon/cart/stretcher. If there’s any movement other than in a vehicle (or stretcher), the whole day does not count as rest.
Also for each Failed Save, the character will remain in a coma for 15 minutes. This can be alleviated with magical restoration/healing/potions.