On day 4 or 5 I too had a severe headache, it lasted for almost 2 days. The way I dealt with it was by telling myself that my body was detoxing something and what happens phisiologically when whatever is being detoxed is being detoxed, is that a headache occurs. I used the headache as a measure of the great affect of the detox instead of thinking that my body was craving something or needed something. My body needed nothing more than to continue detoxing. Just accept and be with the headache instead of trying to fight it.