Aren't dreams suppose to be nice?

I had the worst dream ever last night. I work in a trauma center so I see a lot of people in bad shape. I dreamt that I was called in for an emergency and when the patient arrived, it was someone I knew and care for a lot. It was the worst feeling on Earth. Everything in my dream froze. It was like one of those Matrix scenes where everything stops and the camera spins around the person. I woke up scared to death because it was so real that it felt like it had happened. I was in a daze trying to figure out what had really happened. Whatever happened to nice, sweet, pleasant dreams?