If you are fasting, be sure to drink water with electrolytes in it. YOu can mess up your cardiac rhythms without calcium, potassium and sodium.

I fasted for 22 days once, and have done many week long fasts or so, and I get what you mean. There is a sort of empty (in a good way) feeling, I call it a yawning feeling, you just feel open somehow. Also, the energy you get when your body doesn't have to take 1/3 of its energy to digest the food you normally eat.

But you can't be foolish about it. Electrolytes. Very important.