What is happening with this dream?

I had a dream about zombies starting to come to the earth. But my dream was at the beginning with the very first zombies starting. It takes place in my house. But the zombies don't become zombies from an infection, it's someone or something that sends a signal to your brain causing it. So zombies were starting, and we all knew what was happening. Turns out, when you find out a lot about the zombies and the more intelligent you are, that;s how you become one. It's like when you find out too much they turn you into one. But the weirdest part is the signal that got sent to me. I've never felt anything so real in a dream. I remember it as if it was happening now.I remember the exact picture. First you see a coffin that is placed underground, then you see this weird symbol over it. It's a circle around the coffin with a cross going through it. It's so weird. It felt as if i was awake only for this part. But i didn't turn into a zombie. I don't know why, it's as if i fought through it. But even now when i'm awake, that same picture with the coffin and circle pops into my head randomly. I can't get it out.