Frequent nightmares about TWD

I'm on season 3 of The Walking Dead. I absolutely loved it from the start, but something on the last episode of season 2 freaked me out and I can't even see the reason. I've been having nightmares about being in The Walking Dead ever since, but at the same time I want to keep watching it. Also let me say that these nightmares aren't even exciting, they're always about me running from zombies.

First I thought it was just me being sensitive or because I used to have a phobia of zombies but a friend told me her brother has TWD nightmares every night since he started it too. Then I asked some other people and turns out it's really common?

What is the matter with this exact series? I've watched extreme horror movies and had no nightmares, but TWD is terrorizing me? What is going onnn?