The five-time Grammy winner, 56, said she feared falling off stage after being stricken by a tick in 2003 while horse riding.
She said: “My symptoms were quite scary because before I was diagnosed, I was on stage very dizzy. I was losing my balance, I was afraid I was gonna fall off the stage.”
She was sick with the disease on her $87 million (£72 million) grossing, 113-date ‘Up!’ tour and spoke of the illness in her new documentary ‘Not Just a Girl’.
Shania – born Eilleen Edwards – added: “I was having these very, very, very millisecond blackouts, but regularly, every minute or every 30 seconds.”
The singer’s chronic sickness contributed to her developing voice disorder dysphonia, leading to throat surgeries and therapy.
She admitted: “My voice was never the same again. I thought I’d lost my voice forever. I thought that was it (and) I would never, ever sing again.”
The singer’s struggle also came as she was facing a divorce.
She is getting ready to celebrate the 21st birthday of her son Eja D'Angelo in August, who she shares with five-time Grammy-winning producer Robert ‘Mutt’ Lange.
Check out the trailer for Shania Twain's Netflix documentary 'Not Just A Girl'
But Shania and 73-year-old Mutt’s 14-year marriage ended in 2008 after she discovered his affair with her long-term secretary and best friend, Marie-Anne Thiébaud.
The singer compared the end of the marriage to losing her parents in a 1987 car crash when she was 22.
She said: “It was like the death was the end, a permanent end to so many facets of my life. And I never got over my parents’ death.
“So I’m thinking, ‘S***, I’m never going to get over this... in that search to determine what was causing this lack of control with my voice and this change in my voice, I was facing a divorce.
“My husband leaves me for another woman. Now I’m at a whole other low. And I just don’t see any point in going on with a music career.”
In a bizarre couple’s swap, Shania went on to wed Thiébaud’s ex-husband Frederic in 2011 and their relationship is still going strong.