Hi. It is probably water overload. There are different theories on water consumption, some say drink when thirsty, or drink 8 cups a day , or drink your body weight in oz. divided by 2. I was told to drink 1 quart a day at least and that has been working for me, sometimes I go to 8 cups a day.
You should try not drinking it all at once , spread it out over time.
Hopefully you don't have any medical issues like high blood pressure or kidney, if you have medical issues give your doctor a call. Hopefully you are only having a temporary retention issue. It sounds like your abdomen ballooned out because the bladder is retaining water and that caused your abd to expand.