
- Write your worries down. Research has shown that just eight to 10 minutes of writing can help calm obsessive thoughts.
Remember: Worry is helpful only if it leads to change, not if it turns into obsessive thoughts.

Remember: Worry is helpful only if it leads to change, not if it turns into obsessive thoughts.
http://psychcentral.com/blog/archives/2011/01/20/why-ruminating-is-unhealthy-and-how-to-stop/
When I was young I used to ruminate or brood.Looking back it made me feel terrible.But thinking is not the same as ruminating.And neither change our reality unless we act.To stop ruminating it may be enough to say it does not usually help when you feel down.Then maybe take a walk,look at the world of nature.Try talking to a kind friend instead if you can.