Review Question - QID 213387

A 33-year-old man presents to the emergency department with dizziness. He states he has experienced a sustained sense of disequilibrium for the past 2 days. He feels that the floor is unstable/moving. The patient is otherwise healthy and does not have any other medical diagnoses. The patient is currently taking vitamin C as multiple family members are currently ill and he does not want to get sick. His temperature is 98.1°F (36.7°C), blood pressure is 120/83 mmHg, pulse is 73/min, respirations are 16/min, and oxygen saturation is 98% on room air. Physical exam is notable for a horizontal nystagmus. The Dix-Hallpike maneuver does not provoke symptoms and examination of the patient’s cranial nerves is unremarkable. Which of the following is the most likely diagnosis?