I know my daughter could relate to that demon thing! She had herself so upset and anxious about the fact the she MAY become possessed! She was like that about 2 years, then it subsided and when she went to a local convenience store her receipt said, "$6.66" she flipped out all over again for months. She's fine again, but she thinks everything is a sin! It was pretty bad for a while.
I myself fear those stomach bugs every year (noroviruses, norwalk virus, rotovirus, whatever it may be like that). Last year I heard it was SO bad that I refused to go out to eat anywhere because I didn't know who would be touching my food. I had to go to a funeral in February and they had the dinner afterwards and I was freaking out. Of course no one knew this, I hide it, but I tried to only eat "safe" things that most likely no one touched with their hands (ex: I wouldn't eat the fried chicken because someone probably plated it with their fingers)
telling anyone who was nosy, "Oh I'm not really hungry" (I was starving!) I also have all kinds of health anxiety over cancer, MS, tumors, you name it! One worry stops and another starts, some even overlap. I have to keep checking and checking the thing I am worried about over and over again (well maybe I didn't look at it right a half hour ago, maybe look at it from a different angle, try a different flashlight, feel around for swollen nodes, and on and on it goes. Oh yes, I can relate to you in the health OCD. Too bad my daughter wasn't into posting on boards, she could ABSOLUTELY relate to the religious OCD!