A 34-year-old woman from Delhi presents with sudden-onset hearing loss in the left ear for 3 days, accompanied by tinnitus and mild vertigo. She reports a recent upper respiratory tract infection 1 week prior. On examination, Weber test lateralizes to the right ear, and Rinne test shows air conduction better than bone conduction in both ears. Otoscopy is normal. Audiometry reveals a left-sided sensorineural hearing loss across all frequencies with a 3 dB air-bone gap. What is the most likely diagnosis?