CBT is great for this sort of thing because it teaches you how to debunk fears and deeply held (and harmful) beliefs, essentially, through a variety of techniques. I have taken it in the past for anxiety disorder and really found it helpful. The local mental health team is thinking of putting me through another course of CBT for anxiety and depression (I guess that's the closest thing they have to OCD-specific CBT, and besides I have depression too, among other things).
Talk to someone about it, get some professional help and support, and in the meantime if you can't rationalize with yourself ('this is the OCD talking', etc) just try to distract yourself when it gets really bad. That's all I can do sometimes.