I find that when I am anxious about the day, about my weight loss, and things in general, I take some deep breaths and sit quietly for a few minutes. I find that helps to get me back in balance.
My doctor recommended a book by Jon Kabat-Zinn "Wherever You Go There You Are". It is a lot about meditation, but really keeps you centered in the now. Forget about the past and don't worry about the future, just your life in the now.