Dang...you might be peeing a lot out. But i can't imagine that being the reason for your losing 6 pounds within a week.
I know i've heard you can die from drinking too much...but i just know because someone drank liters and liters for a contest. But like i said you have to be drinking liters and liters for it to actually kill you.
Litres within a short period of time ^_^
My guess is that my studying used a lot of calories.