> Feeling smart != being smart. I was once doing a water fast for a week and felt rather enlightened after a few days, like any problem would be easy. Upon trying to churn on some more advanced math proofs and programming stuff, it seemed to actually be harder than it would usually be.

Exactly. Often touted for silly reasons, but it's definitely 100% true: feelings are not facts. Feeling healthier does not mean you are healthier. Feeling clearer does not mean you are clearer, etc.