First fast ever, 36 hours in.

I started a only Water Fast on Saturday night and was hoping to make it till Tuesdayou morning. Im on Antibiotics right now also. I've been doing great until about 20 minutes ago I started getting very dizzy and nauseated. I ended up throwing up. How do I prevent that? I feel much better now.Also this is my first fast ever, I'm very happy with how it is going, other than the sick feeling.