Sudden hearing loss is clinically defined as when a person's hearing is reduced by at least 30 decibels within a 72-hour period, according to the American Hearing Research Foundation. Unfortunately, not much is known about what causes many cases of sudden hearing loss, as of 2015.
Some people report suffering from sudden hearing loss instantly, while others report that it happens over a period of hours or days, the American Hearing Research Foundation reports. About 66 percent of patients spontaneously recover from the hearing loss without treatment. For others, research has not been able to pinpoint a specific bodily event that triggers sudden hearing loss, but studies have found that some cases are due to various infections or the herpes virus.