A 55-year-old bank teller comes to your office for persistent episodes of dizziness. The first episode started suddenly and lasted 3 to 4 hours. He experienced a lot of nausea with vomiting; the episode resolved spontaneously. He has had five episodes in the past 12 weeks. He does note some tinnitus that comes and goes. Upon physical examination, you note that he has a normal gait. The Weber localizes to the right side and the air conduction is longer than bone conduction in the right ear. Nystagmus is present. Based on this description, what is the most likely diagnosis?