There are lots of things that can cause dizziness.
*Dehydration
*hormonal imbalance (early in pregnancy, right before your period, menopause)
*illness (like the poster above stated middle ear/inner ear)

I have had dizziness from all the above, but I have also had vertigo. There is a medication called antivert that is an Rx that can help w/ the dizziness. Please get checked out and make sure there is nothing serious going on.

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Mental that one, I'm telling you. ---Ron Weasley, "Harry Potter and the Chamber of Secrets"