CW: pain, agony, suicidal ideation Stiff person syndrome (SPS) is a rare acquired neurological disorder that most often causes progressive muscle stiffness (rigidity) and repeated episodes of painful muscle spasms. Stiff Person Syndrome – Symptoms, Causes, Treatment | NORD Like Céline Dion, I have Stiff Person Syndrome. It’s excruciating and especially affects the muscles in…