You have overdosed yourself, over-medicated with water! It's possible and very dangerous! Never drink more than 12 oz of water at a time, the kidneys can only process about 8 oz an hour. Also, you need 1 tsp of salt per quart of water.
If you absorb more water without enough salt, you lower the amount of salt in your bloodstream. If you have low blood salt levels, you will not only get dizzy, you will go into grand mal seizures. It happened to my neighbor who was paranoid about having to take a urine test. He downed a gallon jug of water and next thing you know we had to call the paramedics.