Have you addressed a health issue that resulted in a significant improvement in performance?

Personally, just by eating a good breakfast with meat, very unusual for me -- I was at a tournament in Golden Gate Park IIRC and nearby was a Dutch restaurant which offered something like a steak for breakfast (I normally had cereal or pancakes) and I played noticeably better. (That is, I beat a much higher rated opponent and he had not blundered.)

I guess diet and exercise are obvious, but maybe people have found particular drugs (could be caffeine or more exotic) make a difference.

A lot of people have untreated sleep disorders and I wonder if anyone who started using CPAP or other therapy saw an Elo increase.