I gave up caffeine once for Lent. After about a week, I was getting dizzy spells - it sure is a drug. I survived, though, and really enjoyed a cup of coffee with a sausage omelette when it was all over.
I didn't get the same results the following year when I succumbed to decaf, because it isn't totally caffeine-free. Actually, this year I've had only one cup of decaf coffee and I woke up the following morning with such a headache the following morning. I wonder if actually was decaf.