How to talk to my mom about my husband

My husband is uncomfortable going to Thanksgiving this year because my mom keeps bringing up this embarrassing thing that happened last Christmas and always brings it up Everytime we are around people even though she knows it bothers him. My husband was on medication back then and one of the rare side effects was seizures. Well. He had a seizure. A bad one and I had to call 911. It was at Christmas and his seizure was so bad it caused him to release some bodily functions. My mom brings it up as a joke. When that all happened it left a stain on her carpet and on the 4th of July she showed it to guest to prove her story. She knows it embarrasses my husband and it was a very scary thing for me. My husband doesn't want to go to Thanksgiving because he's always uncomfortable. I know I need to talk to my mom. I'm just not sure what to say. I'm nad at words and confrontation.