Learn to focus on positives. Here is one way to get out of the destructive negative thinking habits. In this case, don't just sit there and worry about it. Go ahead and take care of it. You have control on it.
Procrastination is the root cause for many stressful episodes.
The second situations are those you have no control on. In this case sitting and worrying about it is not going to make any difference in the outcome. So, don't worry about it. Dean Ornish talked about how our culture makes us to dwell on the high stress activities. Now, if this happened in the USA or many other parts of the world, the drivers will be getting out of the car and showering each other with abuses, threats and remind the other person how stupid he was to cause the accident.