Is it possible to have a bad reaction to caffeine after years of drinking it?

I've been drinking coffee pretty steadily for 5 or so years, but just recently I seem to be dizzy and nauseous, and wonder if it's from the daily caffeine habit. I drink about two cups a day. Obviously, I know it could be something else, but if it's as simple as kicking the caffeine, I don't need to get all complicated about it.