and had EXACTLY the same experience. A little lightheaded at first, grumpy, and tired. On the third and fourth day I felt sick/nauseous. But from day 5 on, it got easier and the hunger pangs subsided substantially. I lost 14 lbs. in those 10 days. As I recall, the Master Cleanse also requires you to drink a laxative tea first thing in the morning, and again just before bed. Granger is right...if you feel gaseous make sure you head for the bathroom!
I was advised by 2 different nutritionists, and my sister who is a nurse, that you should have some small amount of protein while doing the Master Cleanse, suggesting that just a handful of raw almonds would be sufficient, but necessary.