[darkwizard42]

Could it be some sort of mental withdrawal?

Some suggestions to help with the tiredness (and I'm grounding this in my athletic background, not a doctor):

1/ Increase the amount of water you are consuming. Try to put down 80 oz a day. Keeping a full water bottle with you on your person will help a lot.

2/ Keep a strict bedtime and sleep 7+ hours nightly. Feeling tired? Get sleep. Building a good set of sleep habits will help your body regulate itself overall better. Also just in general people don't sleep enough and this is a great easy spot to start looking.

These are two tips I know have helped a TON for me. Keeping discipline for sleeping and "over" hydrating have resulted in a lot of my brain fog disappearing or at least my perceived productivity and focus has improved. I also spent more time in the gym but I feel that is a personal decision and the above tips were independently very very useful at keeping me sharper.