I've also had this experience-my caffeine intake used to be quite a bit higher (4+ cans of diet coke plus 3 cups of coffee every day). If I missed one of my regular doses I'd get horrible headaches, but since going HFLC I've completely cut out the diet soda and drink anywhere from 1-3 cups of coffee a day, without any headaches at all. Coffee/caffeine has become something I drink because I enjoy (especially in the morning instead of eating), but I don't rely on it anymore and I don't notice any physical changes if I don't have it.