I also went through this mental stage, which I am sure is fairly common. At age 52 I had a heart attack and triple bypass surgery. I never smoked; ran half marathons; biked 30 miles regularly; not overweight, etc. Went through cardiac rehab and at age 53 I had another heart attack. Talk about thinking I was damaged goods. In my depressed mood my brother gave me some good advice. I could live the rest of what might be a short life feeling sorry for myself or I could play the cards that were dealt to me. Once I accepted that attitude, I am now 76 years old and, for the most part, do anything I want to. I exercise on an elliptical machine 30 minutes daily and then walk for another 15 minutes at our recreation center when the weather keeps me inside. On days I can get outside, I bike from six to ten miles on bike trails. I also play golf two to three times a week.
The point is, I went from thinking I wouldn’t see my son graduate from high school to seeing him graduate from college with advanced degrees, marry, and now seeing my grandchildren in high school and younger. Could I die any day? Yes, but that has been true since age 52. I could have wasted a lot of years feeling sorry for myself, but I refused to do that. Life is what you make of it. Good luck.