Luke, I have seen this before but it usually passes.
I think with prayer and God's Word you will get assurance.

You know I had a room mate in college who suffered from hypochondriasis.
This is a very real disorder, you can read about it here:
http://en.wikipedia.org/wiki/Hypochondriasis

He was always worried about his health, always felt like he was sick or getting sick, always going to the doctor. I wonder if there could be cases of something like "salvation-chondria" (?) ...I'm not suggesting that there is, just thinking and typing...