You're not playing notes or counting or even thinking about the direction of the phrase. Your instrument feels like an extension; it's no longer a tool, because it's part of you. You embody the piece. Time disappears; you can't quite hear yourself anymore, but in this case, that's okay. Somehow, the music is encompassing you.
Moments like that can't happen every day, but when they do... that's when I know exactly who I am and who I want to eventually be.