Earlier quoted context omitted.
This is, distinctly, not my domain. But, curiosity struck and so I went to the almighty Google and found this: https://www.livescience.com/5325-mental-fatigue-perceived-ph... You may find it interesting, so I figured I'd share it. I offer no opinions, other than to say it is interesting and that the study was done with a very small sample size. (I'm unqualified to opine beyond that.)
A lot of research around Chronic Fatigue Syndrome is pointing toward mitochondria as being a prime culprit. As the most energy consuming organ in our body, I would expect the brain to quickly use up our easy-to-access / quick release energy so it's really not so surprising to me. I have no biology degree, but I find it interesting and have no problems opining about :p I've often found a smoothie made with fresh fruit…
I used to be married to a lady who was quite proud of me. Well, so to speak. She used to take me to these fancy parties where people dress funny and eat crap I can't pronounce - they also use utensils for certain dishes and all sorts of fancy stuff.
Well, she'd introduce me as, "Dr. KGIII."
Now, I don't want to say people are stupid - but this frequently resulted in me being asked medical questions. I, being drunk more often than not, would give absurd medical advice.
I've since learned to not opine on anything medically related, as it seems to result in people coming back to me with very angry moods. So, certain subjects I try just let the links speak for themselves. It works.
Also, my method was to remain in a fairly constant state of inebriation. It was surprisingly effective, though I'm not sure I'd recommend other people try it.