Sleepwalker

I woke up on a rooftop, and silence startled me, no cars and trains passing by. There were no people, the whole place was empty, and I could only hear a gust of wind hitting my skin. I recently found out that something disturbing had happened, and you wouldn't believe it, because even me, I couldn't believe it at first. Guess what? There were literally zombies roaming around the city! They are no longer human, but they are purely aggressive as if something had been injected into them. They were already dead, but still.. alive.