Look, it's easy. Go watch First Blood Part 2, Rambo. Commando. Die Hard. Predator...just about any 80's action movie. Or really, ANY action movie, since we have these sorts of heroes today, like John Wick. They bleed gallons of blood. They fight effectively while bandaged or stitched up. While tired and beaten. They may move a bit more slowly, or limp a little, but they perservere.
You suffer actual permanent wounds or fall unconscious when the narrative says you do. Just like how you rarely run out of ammo until it's plot-convenient (Mr. Wick avoids this, but it's pretty common).
What would be realistic is not allowed to get in the way of the story. So characters grit their teeth and function on "super-adrenaline". Even if they are rendered temporarily unconscious, they can have a heroic recovery by rolling a 20 on a death save (Samuel L. Jackson does a fine version of this in "The Long Kiss Goodnight").
D&D evokes these sorts of tropes, which were common even back in the 70's, and tales of seemingly superhuman feats abound in myths and legends. Don't get too hung up on "what is realistic" or "what breaks my versimilitude". You are John Carter facing down a small army of Tharks. You are Conan, nailed to the Tree of Woe, waiting for that darned vulture to get close enough for you to bite it's head off.
You're not "Ordinary Guy #17 getting taken out by a sniper in one hit in order to show your platoon that they are in danger". That's what NPC's are for!
Worry about the ramifications of hit point loss when your theme song stops playing.