A 24-year-old male, previously healthy, woke up with retroauricular pain one morning. After 1 day, he developed left-sided facial droop and decreased taste sensation on the right side of the tongue. He experienced hyperacusis and right eye discomfort. No diplopia, tinnitus, hearing loss, or limb weakness were present. Physical exam: inability to frown, raise eyebrows, or fully close the right eye; left-sided facial droop when smiling; decreased taste sensation on the anterior right tongue. The most accurate diagnosis is: