Headaches due to coffee (caffeine) elimination while doing keto are real for me. They last for a day or two and then go away. I drink about 1 sometimes 2 cups a day, and within 24-36 hours after no coffee, I'll experience a dull headache. They are not intense and are easily managed, and when I first experienced them, I thought it was due to the onset of dehydration. I do not experience this with tea, but I make my coffee strong, so that may be a factor. They have nothing to do with dairy (HWC, I don't use milk) as this will happen if I'm drinking coffee black.