I've noticed lately that my playing normally peaks at about 1 to 2 pm and hits rock bottom between 9 pm and midnight. Anyone else experience fluctuations like this, or is it just in my head?
It might be just your current sleep circle and the hours in which you dont feel tired. But in the end its all in your head.
Most likely in your head. I always tend to come up with better stuff in the evening, but no changes in terms of actual playing.
You might just be tired. You might try drinking some coffee at night and see if that improves your performance.