Sudden Sensorineural Hearing Loss (SSHL), or sudden deafness, is a rapid loss of hearing. SSHL can happen to a person all at once or over a period of up to 3 days. It should be considered a medical emergency. A person who experiences SSHL should visit a doctor immediately.
A doctor can determine whether a person has experienced SSHL by conducting a normal hearing test. If a loss of at least 30 decibels in three connected frequencies is discovered, it is diagnosed as SSHL. A decibel is a measure of sound. A decibel level of 30 is half as loud as a normal conversation. A frequency is another way of measuring sound. Frequencies measure sound waves and help to determine what makes one sound different from another sound.
Hearing loss affects only one ear in nine out of ten people who experience SSHL. Many people notice it when they wake up in the morning. Others first notice it when they try to use the deafened ear, such as when they make a phone call. Still others notice a loud, alarming “pop” just before their hearing disappears. People with SSHL often experience dizziness or a ringing in their ears (tinnitus), or both.
Some patients recover completely without medical intervention, often within the first three days. This is called a spontaneous recovery. Others get better slowly over a one- or two-week period. Although a good to excellent recovery is likely, 15 percent of those with SSHL experience a hearing loss that gets worse over time.
Approximately 4,000 new cases of SSHL occur each year in the United States. It can affect anyone, but for unknown reasons it happens most often to people between the ages of 30 and 60.
Source Cited link: http://www.nidcd.nih.gov/health/hearing/sudden.htm