Coffeine blocks adenosine receptors, and in turn their numbers multiply, reaching an equilibrium after just 2 weeks of regular coffeine intake. Stop taking coffeine, and you're going to feel pain (mostly headaches and rheumatic pain) 18 to 22 hours after your last dosage. Not to mention being sleepy, depressed and so on. The adenosine builds up as usual in your body after you wake up as a by product of normal neuronal activity, but it just keeps on binding to all those extra receptors. Ouch!
Depending on how heavy your coffein addiction was it takes weeks to months to feel like a normal human being again. If they want to mess with that system, good luck. Finding a drug that causes no withdrawal symptons, good luck.