the dream of my brother

This dream means that you rolled into something and hit your face. That's why it was bleeding. The brain, while dreaming, has the ability to create situations that make sense when things don't. It happens in a second. Your dreams last feel like an hour can happen in seconds. It made sense of getting hit in the face by putting a fear you have, expressed in the form of something of importance to you (your brother getting beat up). The important thing is that you chose to help him out and put yourself in danger. It means that you sacrifice yourself, or that you really love your brother. That's all, and it's a good thing.