A big part of Health Anxiety is not only worrying about having a disease (Mine is something being wrong with my heart) but also not being able to cope if the worse was to happen. For example I worry that I'll have a heart attack and no one will be able to save me.
Again from first hand experience with my wife it's not actually as bad mentally as you'd think. Yeah we shed tons of tears and the magnitude of what she is facing is really scary but after a bit you just get on with life. It is what it is.
It's completely normal to fear "worse case scenarios" but I guess my point is that even if these things ever happen (the chances of which are quite low, especially if the doctor has said you don't have anything to worry about) then it's not necessarily even going to be as bad as we imagine in our minds.