I don't know what kind of financial situation you're in, so I'd recommend securing a new job before you quit, but if you are doing fine financially, you may want to consider quitting first. Health is not cheap.

Burnout is a very real thing; personally, I didn't realize I was burnt out until months later, and I just felt nothing. Absolutely nothing. And it's not like you can just flick a switch and make it all okay again.

That said, make a best effort to not burn any bridges and leave as amiably as possible. Good luck!