I am a 14 year old girl who gets a fair amount of exorcise and eats healthy, but when I stand up, even at a slow pace , my vision goes close to completely black and I have to force my muscles to keep me standing. I have also come close to passing out or losing my balance many times, I am worried that i will pass out in a public place or that I am going to hit my head on something sharp. I also drank large amounts of water to see if the symptoms would leave, they did not. I am a 14 year old girl who gets a fair amount of exorcise and eats healthy, but when I stand up, even at a slow pace , my vision goes close to completely black and I have to force my muscles to keep me standing. I have also come close to passing out or losing my balance many times, I am worried that i will pass out in a public place or that I am going to hit my head on something sharp. I also drank large amounts of water to see if the symptoms would leave, they did not.