Dream About Zombie Apocalypse And Escape

I was in the house i lived in throughout middle and high school, but it was two-story instead of single. I was deep into a zombie apocalypse. I had my whole ground level of the house boarded and barricaded off so that hopefully, I wouldnt get overrun. But in my bedroom I had a window that opened over the roof of the garage, so if I ever needed to escape that would be my way out. I was in the middle of cooking some kind of delicious soup. I could smell it. It smelled like Pozole the Mexican soup dish. Then I heard a massive smash coming from the other side of my house. I grabbed my sword I had set down next to me and quickly went to see what in the hell had happened. Some how one of my barricades had broken away, and the zombies quickly began flooding in. I ran back across the house to peek out of the crack in a window and I was completely surrounded by zombies. Luckily, like I said, I had an escape. I grabbed my already packed emergency escape bag, a tupperware container that I filled with my half-done soup and ran upstairs as fast as I could. I shut the door quietly behind me. None of the zombies had made their way upstairs yet so If they didnt hear me they couldnt locate me. I sat there for awhile just staring at my soup and salivating at the smell. As I reached for it, there was a bang at the door. It just kept getting louder and louder. I could see it starting to lose its strength so I made my way to the escape window and tried to open it. It was stuck. I couldnt open it at all. I grabbed a heavy object in the room and broke the glass away. As I began to climb through the window there was a shard of glass still sticking out that I missed and it cut my arm, very deeply. The pain vibrated all through my body. All I see is blood flowing out all over me. I tore off my shirt, wrapped it around my arm and held it there as hard as i could. I turned back to look inside and thr zombies had just broken through. When I woke up I had this massive dark bruise in the exact same spot where I had cut my arm in the dream. But I sleep in the middle of my bed with a pillow on each side of me. How on earth did I get the bruise?