A ghost dream can have many interpretations. You do not connect anymore with your life and the people around you. If you turn into a ghost, it means you want to escape reality.
If the ghost is of a living friend or a relative, it means you need to be careful. This person may be a potential threat. If the ghost is trying to kill you, it means you can now face your past no matter how hurtful it is. If the ghost is choking you, it means your past haunts your current life.