Hi,
This is very comman. Drink plenty of water and keep hydrated. Tea/coffee will also help but make sure to take in lots of water throughout the day and not in big amounts a few times daily.
Also, when you go from sitting, kneeling or stooping posotion, come up very slowly and leave your head bent so it's up last. This prevents it most of the time for me. You may have slightly lowered blood pressure either.
Sometimes I think I'm going to black out but I never do so just keep going with it. I'm starting week6 tomorrow so a bit of dizziness is worth it still.
Good Luck.