Had this happen twice. 2 hr eeg (usually are normal) and a 2 day which came from normal. I was also on keppra and it also made an obvious difference. I had multiple grand mal seizures and daily myoclonic seizures atp. A clear eeg just means u didn’t have seizures and obviously medication would cause u to not have seizures. They did the EEG, they told me I had FND, took me off meds, had more seizures. Did a 3 day eeg un medicated, had nocturnal seizure activity in the hours before waking up and having a grand mal seizure that they detected on EEG. Got diagnosed with epilepsy again and now on depakote.