A 28-year-old woman from Mumbai is brought to the emergency department by her family with acute-onset bizarre behaviour over the past 3 days. She is found talking to invisible people, laughing without apparent reason, and making repetitive hand movements. She believes that her food is being poisoned and refuses to eat. On examination, she shows waxy flexibility when her arm is passively moved. Her speech is incoherent with frequent neologisms. Urine drug screen is negative, and physical examination reveals no focal neurological signs. Thyroid function tests and blood glucose are normal. What is the most likely diagnosis?