"I felt very bad," the 38-year-old French-Canadian diva told The Associated Press in a recent interview. The singer had labyrinthitis, an inflammation of the inner ear often accompanied by an impaired sense of balance.
Dion said she refused medication that could dry out her vocal cords, despite being told it could take her up to a year to heal.
When a doctor said jittery movements in her eyes had stopped, Dion said she "took a chance" and returned to performing.
She told the AP she's "95 percent" better now.
"It's hard to do a show, but it's harder not to do it," Dion said.
Dion will put on her 500th show at Caesars Palace on Sunday. It is a benefit production to raise $1 million for 10 local charities.
The performer said she's excited about the benchmark performance. Some concertgoers have paid up to $10,000 for two front-row seats.
Dion began a three-year engagement at the 4,100-seat Colosseum theater in 2003. She's now performing about 165 shows a year. Her run has been extended through the end of 2007.