When I catch myself fretting, I try to bring myself out of that useless loop and bring myself to a task, no matter how small, that will get me closer to the goal I am fretting about. Of course not all the things I worry about in my life are that simple, but with language learning, it largely is. If I get bummed that I'm not at the place I want to be--fluent--then instead of fretting, I get out the SRS or something that I can do to get me closer. A much better use of my time and energy.