Obsessive thinking may be a symptom of various diorders:
Obsessive Compulsive Disorder (OCD)
People with OCD may have obessive rumination with a compulsion to do things that reduce the distress caused by the obsession.
People with depression may have obessive rumination on negative or depresssive thoughts.
People with panic disorder and panic attacks may develop obsessive worry that something is wrong with their health.
Post-Traumatic Stress Disorder
People with PTSD often find themselves obsessing over the trauma they experienced, or the belief that the trauma will occur again.
People with very severe phobias may start to think about the object of that fear more and more with everything they do.
People with social anxiety may obsess about embarrassing themselves in social situations.
Generalized Anxiety Disorder (GAD)
People with GAD may have numerous repetitive worries.