if your mind gets caught in a circle of negative thoughts, one thing you can try is to go back to your physical sensations. One way to do this is to massage what we call the "switching" points : http://www.touch-sport.fr/blog/video-points-de-switching/
If a particular aspect of your day generates a lot of stress, I suggest you use the following technique, gently touching what we call ESR points (Emotional Stress Release) : http://www.touch-sport.fr/blog/video-antistress-lse/
I apologize for the absence of video in English, but I'm sure you'll get the general idea :)
If this isn't helpful enough to get you out of this negative mindset, and if it's possible for you, a private session with a TFH practitioner is a very powerful way to overcome stress.
More info : http://www.touch-sport.fr/en/