My first water fast, days 3-4 I was very uncomfortable and my body was very "irritated", I was very tired, dizzy, and slept most of the day (which was best!). I could also feel sensations in my stomach and liver, I believe both organs were healing. A massage helps a lot if your body gets irritated and uncomfortable.
Everyone is different though. I think I had it a bit rougher than many people, because of my health and the healing that had to be done. It was worth it though.