This happened to me last Monday. I woke up at 4AM to use the washroom, but stumbled and almost banged into the wall because I was so dizzy and felt nauseous. Unfortunately this feeling lasted almost 24 hours. I was fine the next day.
The only thing I can relate it to was what I ate the night before. I ate at a restaurant and pigged out on greasy, unhealthy food I'm not used to. I guess it didn't agree with me.
Did you eat anything questionable the day/night before?