Just dehydrated?

Dear Doctors,
I am an 18 year old girl, average in size living in new england. Because of the change in temperature of the summer, I assummed that my near fainting/ blurry vision spells were normal and due to a lack of hydration. I drink an average of 3-4 cups of water a day. But then I started to notice that I have theese spells after eating as well. I will be half way through a meal and I will start to expierence nasuea, followed by my face feeling hot, then my vision will loose focus and I will feel as if i am seconds before collaspsing. I havent yet actually lost conciousness but each time seems to be excessively worse. Theese spells will carry out for 1-2 hours before I feel okay enough to continue my day.
I feel a general sense of fatigue through out the day and my vision will go blurry from time to time but after eating is when it is uncontrolable. It feels as if I am on drugs when its happening and lose sense of reality. My vision will focus in on certain objects than back out again as if I was on ectasy. ( i havent taken any drugs in more than a year so I dont believe its side effects just making a comparison). These spells are really affecting my life, Im afraid to leave the house because I dont want to pass out in public, and almost every time i eat it causes a scene. Please help!