J.K. Rowling, author of the Harry Potter stories, has written a novel for adults called the Casual Vacancy. In it she writes about OCD-Obsessive Compulsive Disorder, from personal experience.
The Royal College of Psychiatrists says that one person in every fifty will suffer from some form of OCD in their lifetime.
OCD is usually associated with behavior-like hand washing. Obsessive and frightening thoughts are also under the rubric of OCD.
Read more at this link. It is worth the time.