A 42-year-old woman presents to the ENT clinic with a 6-month history of episodic vertigo lasting 20 minutes to 3 hours, accompanied by unilateral tinnitus and aural fullness in the left ear. She reports progressive hearing loss in the same ear over the past 4 months. Audiometry shows low-frequency sensorineural hearing loss (SNHL) on the left. Caloric test reveals reduced response on the left side. MRI of the internal acoustic meatus is normal. What is the most likely diagnosis?