What Causes Light Headedness Every Afternoon While On Medication For Epilepsy?

I have been getting light headed every afternoon for a couple of weeks now. It's like a floating feeling, like I can't quite concentrate on what I'm doing. I also have mild epilepsy that I'm on medication for, but I wonder if this is a new type of seizure that I'm experiencing. However, this feeling lasts for the rest of the night. I do feel better in the morning but the light headedness never fails to return. I've also been getting a throbbing headache on the right side of my head. I don't have blurred vision or anything like that, I just feel like I want to go to sleep all the time.