Derek Hough found it difficult to watch the ‘I Am: Celine Dion’ documentary. The 39-year-old professional dancer watched the show with his wife Hayley Erbert, 29, but admitted it was hard to see Celine’s battle with Stiff Person Syndrome, particularly her seizures, as it reminded him of Hayley’s health issues last year when she suffered a cranial hematoma from a burst blood vessel and required an emergency craniectomy. He shared a video on Instagram of the couple meeting Celine and wrote: “Watched Celine Dion’s new documentary, ‘I Am Celine’, last night. “We were lucky enough to meet her a cou…