This may not be related, but the "state of mind" thing made me wonder if it might be. I have a couple of vivid memories when I was learning my first instrument. One was when I was in a snit for some reason, decided to ignore my teacher in a huff, and then played very well. I realized that because I didn't care at that moment what he thought of my playing, I played better, and took note of the fact. Another is that we have thin walls. When I played or sang for myself, neighbours told me of being moved, when I had not planned on moving anyone. There seemed to be an undercurrent that not trying to influence the listener or not caring about the listener seemed to have a good effect on the listener.A bit different - two professionals both told me an anecdote where each of them at some point gave up and decided they weren't good enough. At the very moment of giving up, their playing improved dramatically, because what had stood in their way was too great an effort.
Practice like it means everything in the world to you. Perform like you don’t give a damn.