An 18 years old girl presents with several episodes of confusion over the past several months. Typically, she experiences a warning signal, which she describes as a rising sensation within her abdomen that travels upward through her chest. She is usually unaware for a few minutes, but others have told her that she smacks her lips, picks at her clothing, and a headache, and prefers to lie down. She notes that her memory has not been as good as it was in the past, and her school grades have declined. What is the most likely diagnosis?