How do i get nightmares and whats this dream?

A few months ago I started feeling fogged out and like I'm living in a constant fog ( if you get me ) I'm only 15 but still I never have dreams up untill know I have them nearly daily since this fog and I had a dream recently about zombies its my first ever nightmare and it was about zombies! I was in a vault thing and I was with 4 other people and we was running round my village as we had no weapons and we one of us got bitten so we caved his head in with our boots so he don't come back then we got to a safe place ( not so safe ) were there were for some reason naked women walking round and soldiers protecting the outskirts of it and they got in and I got bitten and went nuts like a sleep rage and started bitting the zombies and punching them then I woke up sweating and full of adrenaline and slight fear BUT I ******* LOVED IT!!!! Does anyone know how I can have more nightmares please, any tips? Also wtf was up with my dream?