Pseudoseizures are diagnosed in EMUs with video EEG. You match the behavior with the EEG to see if there are epileptiform discharges that correspond to the episodes. While this is clearly absurd for an epileptic seizure (impossible movements, insane duration, and no postictal period), there are plenty of cases of bizarre seizure patterns that are VEEG proven.
What a dumb question, there's literally a UWorld question about how a girl with a hx of seizures faked one and how you need to do neuro testing if they have no post-ictal confusion. I'm sorry, why are we even entertaining this if she has NO post-ictal confusion?