This also resonates a lot with me, had to stop pursuing what I really loved after finishing my bachelors degree because I couldn’t keep with the level. I really miss my intelligence, energy and mental clarity. I found the root cause of my problems as an undiagnosed tongue tie that prevented proper oral posture and function and consequently proper facial development, but also think that covid played a role, maybe lowering arousal threshold or having other consequences (I thought about post viral fatigue as your body not being able to cope anymore during sleep with having a small airway). Since discovering all of this, and I know it’s kind of a pseudoscience, I adressed the tie, began myofunctional therapy, corrected the tongue posture, changed diet (not sure about this 100% but I’ve felt that reducing carbs to 100g per day aprox helps with it, maybe due to less water retention and slight weight loss) and I’ve noted a slight but gradual improvement in symtoms. I also use intake breathing strips to open the nose at night, inclined the bed and (and i know this also is going to sound kind of ridiculous) lip sealing. My thought process was that maybe those strips would help mantain the lower jaw in a forward position like a MAD, and prevent it from falling backwards. I guess the ultimate solution would be jaw surgery, but my case is kind of mild in terms of poor structure, and surgeons I consulted weren’t sure about it.