This is something I struggle with at work all the time (whether it's about performance or whether people talking about me - I'm paranoid). I have gotten pretty good at stopping the racing thoughts. This may seem a bit weird, but it works for me. I literally step back and ask myself, "Does any of this really matter in the grand scheme of life?" I then imagine just how tiny and insignificant we, as humans, are in this universe. And, I know this is a bit morbid, but it works...I remind myself that we all die in the end. That interrupts my brain racing. Then, I just tell myself, "I can only do what I can do. I can work hard, but I don't have to kill myself or wear myself out." I also know I work very hard (much harder than a lot of my co-workers), and I remind myself that my job is safe and that I am a good worker.