Hypocondriac problems. Help?

I am a terrible hypochondriac, and every now and then i fixate on some illness and stress to myself that I have it. Even though I know beyond logical doubt that not only do I not have it, the chances of getting it are insanely miniscule. Today I'm haunted by the human form of mad cow disease. No matter how I convince myself there's no way I have it, my mind just keeps thinking I have it and it terrifies me. I constantly smoke pot, but I don't know if this is causing my fear or not. Here's another thing, I've been doing things weirdly in the past few days. Like- I say gramatically incorrect phrases (which isn't typical because I typically come of as rather smart and make good grades) I've been doing weird things - for example- I put a paper towel roll in the fridge, or I leave faucets on, and seem to just feel different lately. Any suggestions?