Sudden hearing loss in one ear?

Presuming no trauma: Don't sit on this. In most cases the cause is never figured out (called idiopathic) but the known causes are serious, ranging from nerve infection, multiple sclerosis, autoimmune disorders, a mass, migraines, or vascular events like a stroke. You need imaging and immediate treatment which would be provided at the discretion of the clinician. The rapidity & unilateral presentation are concerning.

See doc: See your physician immediately since you had such an acute change in your hearing. Please do not wait.