They say that "worrying is interest paid on trouble not yet earned." However, what you feel is so very normal. If there is a change, and bad news at that, we feel a need to prepare ourselves for the shock so that we don't go running through the first window pane when it lands at our door step.
That being said, I'm sure that you can look back on life and realize that the things we worry about the most don't usually happen, but rather come at us sideways at 500 mph and completely blindside us. This is not one of those things. You've clearly found this early, your Dr. is doing the preliminary tests to rule out the unlikely event that you sprouted cancer in the last little while, and he expects good news.
If I had any advice to give, it would be to follow the traces of your fear to their logical end. Would this be bad news because a)you don't have a will/insurance/medical directives in place should things go bad or b)maybe there's so much in life that you meant to do and haven't or c)a medical disaster just wouldn't really fit into your schedule right now.
If you can find the root of that fear, then take steps to give yourself that peace of mind. Write out what you want to do most in life "Kades revolving list of 25 things I want to do before I die", get a will in place, and take a look at what resources you would have available to you should you need help to get through things.
Then, come what may, you are still in control and set to handle anything. Batten down the hatches! K. is on the prowl and ready to kick WHATEVER in the tookas! *Pat pat.* You're gonna do great. Lets take a breath and not waste any more time on "what if's" and switch gears to "what I would do if, " it gives you so many more options and confidence in the future... which is bright!
Suggested reading: "The Last Lecture" by Randy Pauch, and anything by they guy who wrote "Everything I Needed to Know in Life I Learned in Kindergarden." Great for living, and living well. :D Lets get going! And perhaps start it all with a bowl of your favorite ice cream. :D