I have the same thing, and mine starts about 6 days after ovulation. My mother also had severe lightheadedness, also, and hers went away as she aged. Anyway, I have NO IDEA what hormone could be out of whack, but it sure is horribly annoying, and makes you feel really cruddy. I was slightly underweight and as soon as I gained about 10 pounds, I don't have as MUCH lightheadednes before my period. I know since I said I was underweight it sounds as if it's related to my eating, but like you, it is undoubtedly related to my menstrual cycle, also. I wish I could give you an explanation, but I need one, too

Hey, you're not alone.