It does happen to some people... The thing is to FIX IT by doing some exercise (be it fast walking, cycling, whatever) starting within an hour of that candy bar... I prefer to start within 45 minutes of something I think may have too many carbs... Then keep it up for about an hour, and you'll likely burn the glucose right off...
That being said, it's not a good habit to be in... for a while there I started thinking I could cheat regularly by just exercising more... it doesn't really work that way, because even with 4 or 5 hours of intense exercise in a day, my morning fasting reading started creeping back up.
So as others said, just pick yourself up and keep on going!