This is really devastating news for her and the fan community, as she has been an idol in Japan since the late 90's and has contributed with her music in several anime or movies.
According to her blog she felt dizzy and sick with vertigo before going on tour and often taking time to vomit in the restroom during rehearsal.
During the 200 Act I Tour, Ayu had caught a cold and an ear infection and instead of taking time to rest she didn't want to disappoint and kept on with the tour. Unfortunately she lost hearing in her left ear by 2008 and since her right ear has been trying to compensate it is now weakening.
Even now, Ayu vows to keep performing, she is quoted saying "The stage is where I belong. It's the only place I really, truly exist. I don't know anything else."
Here a few clips of some anime where her music was used as one of the theme songs.
This is called "Pray" it is from Buddha 2: Tezuka Osamu no Buddha - Owarinaki Tabi
"Connected" is an OVA created completely for this song. It';s set in a futuristic world where cities grow at an intense pace.
"Dearest," one of Ayumi Hamasaki's most well known songs due to it being the 3rd ending song for the popular series INUYASHA.
In another return to INUYASHA, Ayumi Hamasaki's "No More Words" made its way on the big screen at the ending of the INUYASHA the movie Affections Touching Across Time.
Ayumi Hamasaki also lent her music to Capcom's Onimusha. Here is one of the songs, "Startin"