This depends. Some people just are tired, but some live burtn out, I mean like this[1]. In some cases even having much less real work to do, just because being much more sensitive to some specific stressors they have in their lives. Some burnt out, also some genuinely depressed people still manage being (even without proper medication) reasonably functional and live this way for decades. A 15-hour sleep followed by a day of doing nothing can be a relief even though you can't really recover any close to fully this quick.
I get your point and upvote though.