Imagine waking up suddenly deaf in one ear. Musician and composer Richard Einhorn has lived through it.

In June 2010, the 64-year-old New Yorker awoke to his ears ringing.

"The first thing you think of, of course, is a brain tumour or a stroke," he said. At the time, he was in upstate Massachusetts, far from help. So he called a cab and went to the closest hospital.

Doctors eventually told him it was sudden sensorineural hearing loss (SSHL) — a little-known and not well understood condition that affects one person per 5,000 every year, according to the U.S. National Institutes of Health. At that rate, the condition would affect about 7,000 Canadians a year.

What doctors do know: that most people diagnosed with it are between the ages of 40 and 60; that men and women can be equally afflicted; and that it usually only affects one ear.

Einhorn, who couldn't hear well in his other ear due to a pre-existing condition, was left completely deaf.

"It was incredibly difficult to communicate with anybody ... we were doing it with notes," he said. "I wouldn't recommend it on my worst enemy. It was really, really terrible."

Dr. James Bonaparte says if you wake up with ringing in your ears that continues throughout the day, or if you notice a drop in hearing on one side — and you don't have a cold at the time — get checked. (CBC)

Doctors don't know too much about what causes SSHL.

Dr. James Bonaparte, an Ottawa head and neck surgeon, says there are a number of theories, including viral infection.

"We've done pathology, looked at the ear, and see damage consistent with a virus," he said. But he says it can also be due to an autoimmune or rheumatological problem, in which the body's own immune system damages the organ of hearing.

Emergency condition often unrecognized

The condition can easily be mistaken for a sinus infection or even just a bad cold, said Dr. Vincent Lin, a head and neck surgeon at Sunnybrook Hospital in Toronto.

"One of the difficulties for people to realize is that this is different and this is truly a otologic emergency."

Treatment for SSHL is usually a combination of oral steroids, like prednisone, as well as steroids injected directly into the eardrum. Most people will recover some, if not all, of their hearing within a few days.

Both doctors agree, timing is everything: If a person isn't assessed and treated within two to four weeks, the hearing loss can be permanent.

Bonaparte says pay attention if you wake up with ringing in your ears that continues throughout the day, or if you notice a drop in hearing on one side — and you don't have a cold at the time.

A doctor should check for the presence of fluid in the ear, and a hearing test may be required.

"If you get prompt treatment … the chances of getting your hearing back are much higher," he said.

Music 'doesn't sound as powerful'

Richard Einhorn says his quick action, and the astute diagnosis of a physician, contributed to some hearing recovery in his affected ear. But it's distorted. "It literally sounds like a science fiction robot screaming in my ear," he said.

Einhorn now wears hearing aids, which he says work well in quiet areas. For louder places, like restaurants, he uses a headset and an iPhone he's modified with a directional microphone.

Einhorn's career as a record producer and engineer ended, but his composing hasn't been affected by the hearing loss. Over the years, he has written orchestral and chamber music, as well as film and dance scores, and he is about to start work on a large opera. Composing, he says, is really imaginative work in your head.

"What this is is an inconvenience," he said. "Music doesn't sound as powerful as it used to — and that's a real shame. And I miss it deeply."