I have migraines and chronic fatigue. I'm always dizzy to some extent. If I am sleep deprived, my dizziness often is worse. Heat will lead to it as well. If I sleep without my fan on, I am at an increased risk of dizziness. What kind of dizziness do you feel? Is it more like vertigo(like you spun around a bunch or got car sick..often times things appear to move around)? Or is it more of a pressure in your head type of dizziness, almost like the leftover effects of vertigo?
It could just be a weird one time thing. If you've never had it happen before, I wouldn't worry too much about it, unless it continues. I do know that sometimes excessive earwax buildup can cause this. If it were to continue, I'd see a doctor. As them to look for excessive earwax. As someone else said, anxiety can also cause dizziness.
Edit: Dude, I just realized that you said you woke up at 8pm... Oversleeping can definitely cause dizziness, as well as a headache.