The chatter inside your own head can be distracting beyond belief! I think the trick is to acknowledge the disquietude within your mind, and then bring it into alignment with what you’re actually trying to focus on. My solution is to make that inner voice go to work FOR me, instead of against me by making my inner voice count out loud in my head or singing lyrics (real or my own) to the piece I’m playing. I keep that voice so busy helping me play that it doesn’t have time to whine about how a cookie would be really good right now, or how this passage is really scary. Hope this helps!