Another interesting perspective I have heard describes burnout as being an imbalance between what you want to do/work on vs. what you have to do/work on.
Similarly, while we like to think of “self care” as part of the cure to burnout, self care does not necessarily mean eating right, exercising, etc. Those things are important and may help, but self care also includes things like living a life consistent with your values, finding time to fulfill work that is viewed as meaningful/aligned with a purpose, etc.
The article linked below is worth the read if you’re interested.
There are certainly other ingredients than just overwork (despair, low project morale, lack of stewardship, blame culture) that make people fizzle out. But working too much is there in all accounts.
To your point regarding "burning", flames burn at different intensities and temperatures based on a variety of factors (e.g., material being burnt). The fact that a flame is burning, or has stopped doing so, is not indicative of a specific intensity.
It's not like general workplace toxicity, heartbreaks etc are not equally huge personal problems of their own, but that's why they have their own names.
And to some extent, they are. But to let an employee go and send them on a quest to fix their personal issue is such a very easy distraction from more systematic causes. No need to fix work culture if it was just that one person. No need to question social norms that might nudge people into working an unhealthy number of hours. I guess this is a good day to think about this.
Personal opinion, but where I think many may begin to really suffer from burnout is when they feel like they cannot do anything to improve or change their situation, and that it is futile to even try.
If nothing else, self care is something an individual who is struggling can control in the midst of a bunch of things they cannot.
But when you say "extremelly stressing work," I guess you're not enjoying it. :)
And well, I felt physically OK for 3...4 years. Psychologically not OK, but physically OK.
Until one day, I wasn't anymore.