|MadSci Network: Medicine|
I want to make it perfectly clear that my comments should not be taken as medical advice. I am not a medical doctor, and even if I was, I could not accurately determine the cause of a hearing problem without personally examining someone. Anyone who experiences sudden onset hearing loss should see a doctor immediately.
Acute hearing loss has an extremely large number of possible causes. In most of these instances, only one ear is affected. Some of the causes are fairly benign, such as an obstruction of the ear canal (wax, foreign object, water, etc.). Other, more potentially serious causes include diseases such as mumps or measles, damaged eardrums, very large doses of certain antibiotics or aspirin, ruptured blood vessels, Meniere's disease, or a head injury. An otolaryngologist can determine a particular cause by giving a thorough exam of the ear, nose and throat. In many cases the hearing loss is treatable, especially if diagnosed early. The specific treatment would depend on the specific problem.
The Boys Town National Research Hospital is well known for its high quality contributions to the field of communications disorders. They have extensive information about hearing loss and hearing testing at their web site.
If you have any questions or comments, or would like a list of the references I used to construct this answer, please send me an email.