When you experience burnout, it’s not due to muscle fatigue or lack of sleep. Burnout happens when you aren’t getting something that you need psychologically, over a long period of time. Then the psychological deficit begins to have physical symptoms.
I experienced burnout quite a bit in the first half of my life; hardly any in the second half. I’m 57.
The advice I got that helped the most is to listen to that little voice in my mind that was telling me “stop, I don’t like this!”
Also, I learned that when I am helping people and I feel respected in what I do my mind will happily endure whatever must be done.
Burnout is the result of a spiritual vitamin deficiency. I realize that is a metaphor for “chronic cortisol poisoning” or some biochemical thing, but the solution is to discover and stop the dynamic on the level of your mind.