You might want to look into cognitive-behavioral therapy (CBT). In my opinion, CBT is very effective for the treatment of anxiety disorders, OCD, PTSD, and any situation that invokes negative, intrusive thoughts.

CBT, basically, consists of two parts: Gradual exposure to anxiety-provoking situations, and a focus on thoughts when in these situations.

I don't believe that CBT is an end-all therapy; it simply is a tool in the mental-health toolbox. Another tool, as mentioned by lilodian4ever, is exercise.

I hope this helps.