You are experiencing detox symptoms. If you were to fast on juices, you could support yourself nutritionally and emotionally to a much greater extent. I cannot recommend a Water Fast to any but the cleanest among us!
The first week of any fast is always the toughest. A way to ease this is to do a pre-fast diet of fruits and vegetables, for up to a week. Eliminate all caffeine, sugar, breads etc. etc. Just fruits and veggies, lots of fresh water, and juices. Fruits in the am/veggies pm.
And of course, you should do a colon cleansing routine each day you fast to help your body take out the trash!