It's been a year and a half since the French-Canadian singing superstar Celine Dion announced her diagnosis with Stiff Person syndrome (SPS), a rare neurological disorder that can cause spasms so bad it can break bones. 

Now, in a new documentary, called I am: Celine Dion -- one of the best selling musical artists of all time shares an intimate view of her struggle with SPS, including a harrowing scene that shows her in the full throes of a spasm.