D&D is specifically a system without a death-spiral/injury system because hp doesn't associate directly with a wound.
A fighter with 50 hp gets hit with a dagger for 4 points of damage. We say "ok, that took less than 1/10th of the PC's hp, it's a superficial wound." The next round, the fighter gets sneak attacked by a rogue with a dagger for 26 points of damage. Significant hit right? Better than half the fighter's hp. Still the same type of dagger, so what changed? How did the rogue get 26 points out of a 1d4 dagger, and what did it do the fighter to take five times the damage?
We say, "well, the rogue is a master of anatomy, and he got a blow that made some grievous wounds." But the fighter isn't suffering from any grievous injury. He doesn't have any broken bones, ruptured organs, internal bleeding, or the like. He isn't blinded, stunned, or even knocked prone. In fact, he's fine enough to action surge and bum-rush that sneaky little bugger who backstabbed him, even with 60% of his total hp gone.
Which all goes back to point: Attack rolls, AC, saving throws and HP damage don't represent anything in the fiction directly, and there is no one correct way to narrate it. HP is meat? Explain how a fighter who took a dagger wound can use second wind and heal it up. HP is luck? Explain how rogues are the masters of defeating other's luck? Healing to full doesn't matter narratively because HP doesn't matter narratively, all that matters in the intended action (I attack, I cast fireball, etc). The resolution (the roll vs AC, the saving throw, the HP damage) does not. Its but a means to figure out who lived through the encounter. Flavor it how you like.