When you are on water only you experience lack of energy, especially in the first 2-4 days before you reach ketosis. But combined with urine, i read you have more energy and feel better. They attribute this to ketones; it may also be all those minerals, vitamins and other substances in urine.
Nausea from fasting is normally mild nausea and it goes away by itself or by drinking something. Its not like nausea from bad food, far from that. If you experience it, you will understand. Also you must know its always temporary and it wont last all day. It may occur few times daily. Depends on your body and toxins. I had more problems with it since i was burning fat with all toxins stored so maybe you wont experience it as much.