DEAR MAYO CLINIC: I just turned 45 and am dreading my first colonoscopy. Why do I need to be screened if I’m not having issues? Can you walk me through the process? ANSWER: Feeling anxious or afraid surrounding a procedure, particularly when you’ve never done it before, is completely normal. The purpose of screening is to act before someone develops symptoms. If we’re able to identify polyps, which are precancerous lesions in the lining of the colon, we…