The thing that scares me the most is how time passes by so quickly. In being older, time seems to go by faster. Meaning that death, or having to suffer with something before death, is coming closer to me. There's a line in a song that says, "as far as my eyes can see, there are shadows approaching me" *.
I agree with what Nonightowl had to say about - no matter how well you take care of yourself, something can still happen.
* "Old And Wise" by The Alan Parsons Project from the Eye In The Sky album. Sung by Colin Blunstone, who was a former lead singer for The Zombies.