Why do you suspect that? You'd certainly be atypical as you seem to be aware that caffine is a stimulant (watch the caffine junkies in an office first thing in the morning) and it's drunk to stay awake.....unless it's causing you any problems I wouldn't lose sleep over it (though you're not are you? :>).
Not washing down huge lettuce sandwiches with it are you? ..and smoking fags? while being fat and unfit, plus a coupla valium type downers for stress, - that would probly make for a coffee cocktail sleepytime. [I take that sort of coffee break - great stress reliever] :-)