Not FIREd, but mostly retired.
I don't even want to consider how my body and mental health would have ended up had I not left full time, gruelling work in my 30s.
I was overloaded though. DH on the other hand isn't at all overloaded by his job, he exercises quite a bit daily, could give or take alcohol (as in, he doesn't drink for stress relief), sleeps well, meditates, and is healthier and happier than he's ever been.
It all depends on whether or not you are able to craft and sustain balance. For me, dropping the majority of my work was critical, but for him, I seriously doubt working less would cause any improvement to his health.