I'm going through this right now as well. For me, it's my allergies. The pollen in my area is very high and my allergies are horrific. My head and ears get all congested which cause dizziness/lightheadedness. I then take Benadryl which lessens my allergies but makes my dizziness worse. It tends to be worse in the morning and at night. Also, if you read the side effects of Benadryl, a big one is dizziness.