mrcem2-0325

A 45-year-old man presents with a 4-day history of dizziness. It started suddenly in the morning upon waking, and he is currently unable to get out of bed and is lying still. The dizziness symptoms are worsened by moving and he has vomited multiple times. He had a viral upper respiratory tract infection last week that has now resolved. He has never experienced dizziness before. On examination, he has an unsteady gait, slightly reduced hearing on the left, and prominent horizontal nystagmus to the right. The Hallpike maneuver was negative, and Weber’s test lateralizes to the right.
What is the SINGLE most likely diagnosis?