May be simple. May be related to something as simple as ear wax impact ion. See your doctor.
Still an enigma. Sudden deafness that occurs in 24-72 hours, can be due to a viral infection, vascular occlusion, auto-immune disease and head injury for example. If seen by an otologist early, intra-tympanic injection of steroids or high doses of oral steroids may help. There is also some evidence that sudden deafness may be a genetic disease.