Checking stress levels sounds very sensible. It might be kind of obvious, but burnout is blind denial of the obvious until you catastrophically break, so anything that'll help you get a clue is good.
I've had EMTs and a close friend order me to stop drinking Red Bulls on top of coffee, because the docs thought I was going to die on the spot. I refused to go to the hospital, I had work to do. I agreed to throw away all the Red Bulls, and did, and never went back to them. It took that: I knew I was wrecking myself, but of course it didn't matter.
I'm sure if they'd checked my cortisol levels it would've been 90% cortisol instead of blood. If something like that is leverage enough to get you to stop, check the cortisol levels! :)