Trust me alot of us know how you feel. It's something that I'm afraid only really improved with time. My guess is that you are now being monitored with more regular follow ups? Try and take comfort in that if so....because if something did happen it would be caught early.
You could also try ringing Jo's or Macmillan. Or even ask your doctor to refer you for some counselling. Sometimes getting it off your chest to a complete stranger can do you the world of good.
I too am in a similar boat....I am convinced something is still wrong following my treatment last year so I know how you feel x