"I have a phobia. My doctor has been mad at me for the last 6 years because I refuse to subject myself to a colonoscopy."
My Dr. strongly suggested a colonoscopy and when I hesitated, thinking up an excuse, she mentioned if I choose to neglect the procedure I may be better off finding another Dr. I knew her well, and respected her as a doctor... so I asked her why she was so adamant about it.
She told me her dad would still be alive if only he'd have the test done! He was in his late 50's. I had her proceed with the necessary paperwork.
Your fear can be imagined or real, but the pain your family will feel, if there is something that can be corrected and not, is much greater. Don't be so selfish.