Happened to me years ago, kept thinking it would sort itself and about a week later was in a hospital for a dental visit so thought I'd also pop in to the ENT department. Sound test done by the doctor confirmed 100% hearing loss in one ear. The Dr prescribed some oral medication and complete rest and fish only diet. The Dr (an elderly lady) had captured my undivided attention when she said, its not the outer or mid ear, but perhaps a tumor inside my inner ear.
Canceled all work and appointments and with the diet change I was back at the hospital seven days later, tested and hearing was over 95% recovered.
Dr said it was a remarkable recovery and asked what it was that I'd eaten over the past week to achieve this result.