The dream scene is at work, which shows that you are very nervous, and what you said later, such as you killed someone, should be what you did and saw later, which can't linger in your mind, leading to your dream.

If you have been having related dreams, I suggest you see a psychologist. If you only have it once or twice occasionally, you are too nervous. Try to do something else to relax yourself (listen to music, chat with others). Happiness and comfort are the most important things.