Honestly, I never attempted, headcanon wise, to chalk it up to anything. I think it's just one of those things that you have to chalk up to working within the confines of episodic television and move on. I mean, we could go through similar analyses of Kirk, Sisko, Janeway, et. al. Heck, Uhura literally had her memory wiped and and was apparently re-educated and back at her post in a week.Many of us have just chalked it up to futuristic healthcare being overall better enough than ours to make that possible, & some of us find that rationale underwhelming. So let me break down the chief tragedies that have happened to this poor guy & see if we can't better justify what the outcome was.
I understand that trying to find explanations for things is what we Trek fans do, but this scenario is so outside the realm of realism that I always have to fall back on the Mystery Science Theater 3000 approach: repeat to yourself it's just a show, I should really just relax.