It's completely normal to feel sick if you drink an entire gallon of water in one sitting. Drink water throughout the day.
Also, as long as your urine is clear, or at least not dark, you're probably ok whether you've consumed a gallon, less, or more. My job requires me to wear a suit and I usually carry a briefcase. I'm not going to walk around with a gallon of water in my free hand. So, it's hard to know whether I've drank a gallon or not. I just make sure my urine is clear and make an effort to drink water with every meal (at least once every three hours)
P.S. Sodium causes massive bloating for me. Try to keep it minimal.