What does it mean when you dream your dead mother is crying and you hug her?

This dream is expressing your own grief over losing your mother. Because you know that she loves you, you also know that she would be terribly sad to be taken away from you by death. Your mind puts all of this together and produces a sad dream that illustrates it all. The important thing to understand is that the dream shows your own sorrow. It does not mean that your mother is actually sad or suffering in the Afterlife.