wow this could have been written by me
I also suffer from that nighttime eye pain, and extreme blurriness, not blindness though. I'd wake up and my eye or eyes (usually one eye would be worse) would feel like it hurt to open it and then burn like acid was in it.
I also have a parched and dry mouth like something suctioned all the fluid out of my head. I would splash water in my eyes and rinse my mouth out and that would last me ok the rest of the night.
I don't drink near the amount of water that you do but am trying to do better. It certainly doesn't sound like you could be dehydrated
My eye doctor said I have dry eyes and gave me different drops to try.
Believe me I've tried them all and favor Refresh Plus in the vials, the ointments burn my eyes but I try to use them anyway at night.
One thing that has helped me IMMENSELY and I want to share is this:
At night I sleep with a damp wash cloth on my eyes (I sleep on my back obviously) and I'm not having the dry burning blurry eyes when I wake up. I know a lot of people use fancy eye masks and that would probably work better but I'm just happy to have found something that works and hope this might help you. Good luck, and please post again if you doctor finds something else contributing to it, but hopefully it's something that you can work with.