it could be the dose, but it could also be the migrianes. I also suffer from migrianes so I know what you are talking about. Also I take lexapro and often since I am taking 20mg have suden dizzy spells that usally last only a few seconds, so I oftenwonder if they are related.
I don;t know if this helps at all, but I thought i would at least respond with what info I know.

Dar