Coffee after 5 o'clock?

Who would have thunk it! I never would have thought of myself as an all day coffee drinker, but now, I think I am. Back in the day, caffeine used to have the reverse effect on me, the more I drank, the more tired I became. Now, I get the nice "buzz" and then it wears off and I crash, but I get another cup! It's like I need to get my "fix" or something. Is it laced with crack? Must be, because I LOVE THE STUFF!