How do I stop being such a hypochondriac?

I seriously worry about EVERYTHING. I get an open wound and was convinced that I had HIV I saw a laser (indirectly) and was convinced I would go blind. I freaked out about getting pneumonia and scared about having MRSA. Headache- brain tumor. Stomach ache- stomach or pancreatic cancer. Eyes are uncomfortable- I'm gonna go blind. Ears itchy- I'm gonna go deaf. Now I'm currently obsessing about getting a brain tumor because I ate 4 pieces of sugar free gum which contined asphratame.