As adults we try to monitor and control what our young (and even older) kids watch on t.v., on the computer, read and the movies they see for their protection and to prevent their nightmares and fears.
You loved ones dreams involve 'zombies' and being chased or the family is attacked, etc. I don't even know anything about 'zombies' (seems to be an 'in' thing on television and the Internet, tshirts, etc) I don't know anything about them nor do I want to... I've had so much trauma with death and dead bodies that I cannot even go near such nonsense because it triggers me. If I watched any of that stuff I'd be having night terrors and screaming too. I bet he knows about zombies, has seen shows, etc.
*As adults with trauma we need to monitor ourselves with what we expose ourselves to, just like we monitored our kids. I didn't used to and it made me sicker. I went to a couple different movies and ran into trouble. I went to a war movie (always liked war movies) and it shook me up so bad that when the movie was over I stood to leave and I started crumbling to the ground, I felt like my mind was crumbling and I literally thought someone was going to call an ambulance, so I'm not free to watch what I want anymore or it'll make me sick.
Just like kids watch something scary and it comes back to them at bed or during dreams, it can be like this for adults.
If I watched a zombie show I'd probably be night terroring for a while. We think we're all tough and can handle a lot of things but after trauma the mind will do things on its own...