If I go to class without having thought about it at all that day, I will have lost/gained x pounds, or stayed the same.
If I spend the day worrying about it, thinking about it, wondering about it, I will have made myself miserable and . . . I will have lost/gained x pounds, or stayed the same.
If we could change anything by worrying and/or feeling nervous/guilty about it, then fine, but we can't, so we would all be much better off if we stopped.
We all (yes, me too!) spend far too much time obsessing about ourselves and in my opinion we would be far happier if we forgot about ourselves for a while and concentrated on other people/things.
Which may sound a bit harsh, but in reality I am lecturing myself here, not you, and I can be as harsh as I like to me!!!