What Causes Loss Of Speech Post Epileptic Seizure?

I have epilepsy for almost 26 years now and they are still not under control. I have a vns and have taken all seizure medications. I have complex partial seizures and now something new follows the seizure. I come out of the "fog" after, but am unable to talk. It can last for a few minutes to over 24 hours. Do you have any thoughts about what might be happening?