I'm a 15 yr survivor of leukemia, and now a 1 month survivor of vulvar cancer.
Of course the fear is normal, and you need to give your brain time to process everything you've been through and find a new "normal" for you.
I remember that my worst fears intensified AFTER my treatments were finished. Somehow, no matter how awful chemo & radiation was, at least I felt like I was actively "doing something" and could focus on that. When you're done with treatments, it feels like you're walking the tightrope without a net. But it does get easier in time and it's really important to give yourself that time.... it will take a few years and enough "good" scans before your brain will quit raising the alarm everytime you get a pain in your back, or your leg, or are exposed to stupid people with colds...
But as other folks here have pointed out, the choice is yours as to whether or not you're going to let this fear get out of control or paralyze you. I talked to a counselor who specialized in health issues for about 6 months after I finished treatment and it did help. Also joining an internet support group is a wonderful way to vent and face your fears among people who DO know what you are feeling.
And whoever posted the comment reminding us that nobody lives forever made another excellent point. For me, that fear has been positive in that it's pushed me to try things I normally would never have considered - - I learned how to ride a motorcycle the 2nd year after I finished my treatments.
Remember - the point of surviving is not to avoid death because that's impossible. The point is to take to heart how precious life is and how quickly it can change, and do the best you can each day with what you have.
Anna