I have always found the first few days (2-4) the hardest. My theory is that my body needs to switch metabolic pathways between the usual subsisting on food and storing the extra as fat to instead burn the fat. In my case, I get headaches and feel generally low energy and vaguely nausous. All feelings that I know for experience are alleviated by eating - which makes it ever so hard to get started. Once past that I am usually encouraged by the results I am seeing and the desire not to have to go through that transition again to keep me on track. Good luck and you can always start again. I think each person must learn their own triggers and responses to be successful, which took me many times of trial and error - even after a successful fast I still expect some new surprises.