Almost every day I find myself in a dilemma: I can either try to be a little active and risk aggravating my symptoms, or I can rest and eventually become depressed. When I have to be inactive, my thoughts inevitably turn inward, and since I tend to be a negative thinker, this results in depression.

The thinking about debilitating diseases sounds like it has an obsessive-compulsive aspect to it. The most effective long-term strategy for dealing with this sort of thing is to work on accepting these unpleasant possibilities. If you do research online or try to "prove" to yourself that you don't have a disease, you will be unsuccessful and the anxiety will become worse.

Alternatively, if you can work on accepting the uncertainty and living with the possibility of having some other condition, the anxiety will eventually go away on its own. The general idea is to expose ourselves to our fears--to go toward what we fear rather than avoiding it. This strategy is difficult--entire books have been written about it and it takes many people months with the close supervision of a therapist--but it works.

If you're already stuck in a cycle of rumination, then distraction is a good technique, but the activity you pick has to be something that fully engages your attention (perhaps a crossword puzzle or a conversation with a friend or family member). Kristara's suggestions are good ones. If it's a task that you can do while thinking about something else (like washing the dishes), then it probably will not be effective in distracting you.