I am another one who got horrible migraine-type headaches when I first moved onto decaf. drinks. It took me a week to make me realize that it was the lack of caffeine that was causing it, as my body had become addicted to it over time.
Since then, I have drunk normal tea at breakfast time and decaffeinated the rest of the day, and that works ok for me. On the odd occasion that my routine is disturbed and I don't get my breakfast caffeinated drink, the migraine can strike again by afternoon!
Having read this thread, I have decided that I will give Red Bush a try as a healthier alternative to my usual decaf. drinks.