Am i being mean by not letting my son see a horror movie with his friends?

My son's(16) friend is having his birthday and he invited my son to see a horror movie. I forgot the name but it's about cannibalism. I told him no. Hear me out. He has issues with night terrors. He sees a therapist and he doesn't have them too often anymore but whenever he watches a scary movie even if he doesn't really get scared, he has night terrors about it for weeks and ends up weeing in the bed for weeks. I avoid that if I can. My son thinks it's unfair and I'm not trying to be unfair. Do you guys think I'm being unfair? Be honest