Answered on Quora:
Do people with OCD enjoy thinking about their obsessions, or is it always an involuntary/unpleasant experience?
Actually enjoying your obsessions (or repetitive thoughts) is a rule-out for OCD. If you enjoy your repetitive thoughts, OCD is literally ruled out. I sometimes come across people who enjoy their repetitive thoughts and think they had OCD. I told them that they did not.
Most common differential diagnoses were Prodromal Psychopathy (person is developing psychopathy but does not yet have it), Pedophilia, GAD and Obsessive Compulsive Personality Disorder. Also things like Homosexuality which are not even illnesses. None of them are common. The only one I have seen more than once was Pedophilia.
But by and large, people who come to me suspecting they have OCD are correct almost all (98%) of the time. Clinicians despise self-diagnosis and say it has no credibility, but with OCD at least, many persons are quite certain that they have it, and they are correct in their self-diagnosis.
Usually what happens is they get symptoms and cannot figure out what is wrong with them, so they start doing research. They come across articles that describe OCD in great detail or are case histories of OCD’ers. They read that, and something instantly clicks. They say, “That’s me exactly! The person who wrote that could have been crawling around in my brain reading my thoughts.”
Pure O OCD symptoms are remarkably similar. I also like to say I can spot Pure O OCD symptoms half a mile away, blindfolded, at night. That’s not true, but you get the picture. It’s like they are all “reading off the same script.”
The symptoms are so clockwork-like that it has led me to think there is something wrong with a person’s brain who has OCD. The symptoms are classic, almost all of them display the same core symptoms and you can go down a checklist to figure out who has it, or just recognize it by sheer intuition. In that sense it is very much like how physician diagnoses a physical illness he is familiar with quite quickly via sheer intuition. In that sense, OCD resembles a typical physical illness very much.