I wake up during the night feeling really dehydrated and really hot and nauseous when room is cool and i drink a lot before bed. what could this be?

Hard to say: Could be lots of stuff. Are you running a fever? You could have an infection. Do you urinate very frequently? Could be a sign of diabetes. If it is happening for more than a night or 2 your should speak to your doctor and get checked out.

More: More info needed possibly some tests for thyroid

Benign: The symptoms you are describing aren't cause for alarm. It could be that you ate something that didn't sit well with you. Perhaps you are coming down with a mild infection. I would watch it, if getting worse you can contact one of us.