What is this Stiff Person Syndrome that Celine Dion has?

Dion performing on the opening night of her world tour ‘Courage’ in Quebec City, Canada, in September 2019. The songstress had to cancel her remaining tour shows for 2023 and 2024 due to being diagnosed with Stiff Person Syndrome. — AFP

Most people have not heard of Stiff Person Syndrome because it is very rare.

It is an autoimmune disorder that affects your neurological system.