Since I have been diagnosed, I have bad health anxiety, too. Any ache or pain I have, I think it is going to be something horrific. I agree it can be difficult to keep in check, but we have to try! Stress can only make things much worse.
I have been having abdominal pain almost daily and I was very concerned. But I had a lower bowel series, and though my GI didn't review it yet, the doctor who performed the exam said everything looked fine. So, I know I have to leave the dark thoughts behind and not obsess about it. Therefore, if you got a CT of your head and nothing showed up, you need to let it go. I know it can be difficult, but you will cause yourself more damage if you don't. And if you can't, as Rebecca said, you may be battling anxiety that you aren't able to control and you may need to take medication to help alleviate your stress.