my head the night before? 
yeah that’d be a very busy place! Wanting to do well, desire to impress, competitiveness, performance anxiety, fretting about what might happen, what I didn’t prepare for, what I might have done to prepare better. yep. busy busy busy.
Showtime? that’s different. When it comes down to it, audience or video, just your trainer or a stadium full, when it’s time to do the deed, all you can do is bring yourself 100% to it and be really present with the action.
I used to tell my students - once you’re on stage, once the competition starts, it’s too late to get any younger, fitter, taller, smarter, better looking, more talented, or thinner. It’s to late too train more, plan more, or rehearse more. All you can do is bring what you’ve got, be fully present, and give everything you have with joy, passion, responsiveness, focus, and love of what you do. That’s always going to be enough. It has to be. It’s all you have.