Doctor Proctor
First Post
PHB p279, Ongoing Damage: "You make a separate saving throw against each damage type."
You are suffering ongoing poison damage; you make a saving throw against the damage type, "poison".
-Hyp.
The point that the poster was trying to make is that you don't stack the damage. Just because you're already suffering from 5HP/turn damage doesn't mean you ramp it up to 10.
And using a similar mechanic you just say that after an extended rest you have x less surges until you take another extended rest. So this way, you can still have that mechanic of tracking it, but not punishing the player unnecessarily for losing all their surges.