Hi jim..you sound like you have the same as my son...it's known as pure "o" where you constantly think..replay and replay and replay somethought in your head..driving you crazy.
Usually something or someone will trigger it, for no reason and off you go..giving you a numb headache which is always there......does this sound like you?
My son has had it for 10 years before he was diagnosed..he then did lots of research on the pc and then practiced CBT which can be very effective if done correctly. None of the pills do any good but he takes FLUOXATINE to take the edge off of it.
He now avoids situation that may lead to a trigger but this isn't always practical so when he does trigger he just keeps himself to hinself and waits for it to clear, usually about a week sometimes less, trouble is sometimes it can trigger straight away for no reason.
Stress is a big factor ....if he's worried about an appiontment or having to go somewhere this can also start him off, memory is affected and over analizing is also a factor.
If any of these symptons sounds like you go visit your Doctor who may refer you for some help.