A 26-year-old woman presents with recurrent episodes of déjà vu, epigastric rising sensations, and brief loss of awareness. EEG shows epileptiform discharges in the right temporal lobe. She is started on carbamazepine, which successfully reduces her seizure frequency. However, during a follow-up visit, she reports excessive sleepiness, dizziness, diplopia and difficulty concentrating. Which of the following is the most likely cause of her symptoms?
