A 26 year old woman presents with epilepsy from an unknown cause. She has already seen two neurologists who have been unable to make a diagnosis. For the last two years, she's had daily episodes of witnessed seizure-like activity. The episodes last around 5 minutes with variable motor activity; she thrusts her pelvis out, writhes and trashes, rolls from side to side, or arches her back. During an episode, these motor symptoms wax and wane. Her eyes are always squeezed tightly shut. She sometimes makes vocal noises. She has never had incontinence, cyanosis, or tachycardia with these episodes. She awakens rapidly and reorients quickly without a post-ictal headache. She sometimes recalls what happened during the seizure. No one has noticed any episodes while she is asleep. Antiepileptics have not worked to decrease the frequency of symptoms.
Physical exam is remarkable for profound weakness of the patient's left arm. She barely moves it antigravity and can't exert any force against resistance. When you ask about it, she just shrugs and says "whatever."
Challenge: What's going on?