Levetiracetam - could ther be side effects switching from a different manafacturer of the same drug?

My Highly sought after Neurologist told me that there is a difference of + or - 15% in medication when you go to a generic drug and that is acceptable by the FDA. He put me on Keppra, however my insurance would not pay for Keppra they would only pay for Levetiracetam. Since my seizures are difficult to control he wrote a letter asking that I be given only Keppra because the -15% in medication could actually leave me open to a seizure. My insurance refused to pay no matter what he said. So now after 4 years on this medication I am beginning to have dizzy spells, panic attacks and a reduced seizure but a seizure right at a time when I am caring for my mother with dementia. Not good timing. Pharmacies look for the "best deal" on medications but I am frightened not knowing if each new generic I get is real or a fake thrown on the market.