Water, Water Everywhere and Too Much to Drink

So I have not been feeling well and thought I was extremely dehydrated. Genius me decides to combat this "dehydration" by sucking down water like, well, wine. I go from drinking my normal amount--probably about 75 ounces a day, I've always drunk a lot of water--to like 200 ounces a day. Just yesterday, during the course of my 50-minute session on the elliptical trainer, I consumed literally 75 ounces. I kept sending dad to refill my bottle. I wasn't sweating, and normally I'm a sweater, so I figure, the more water, the more likely I am to sweat it out. This has been going on for a few weeks now; I work out, I don't sweat a lot, so I drink more water. Then after I workout, each time, I begin to feel really lightheaded, like I'm on drugs or something. I've been chalking it up to dehydration, cold medicine, etc. I could not have been more wrong. Go to the doctor today, a family friend, so I totally trust him, unlike my ghetto, HMO docs in NYC. He tells me I've been drinking TOO MUCH water and THAT is why I'm feeling so weird and lightheaded after my workouts. The point here, cause I know nobody gives two shits how much water I drink, is that it is actually possible to drink too much water, FYI. I never knew that. You learn something new every day. Yes, Jacksonville really is this boring. And apparently, 64 ounces a day really is the magic number. Girls, this is why I've been feeling so weird when we're out!!! Phew!