who can help me?

Every night, I will be knocked wake. But nobody is there. It just happen again and again. I don't why. It is true. But my parents still can hear it. They just tell me it is night mare. I don't know is it true. But it real annoys me very much. I am scared and don't know how to do with it. who can just tell me why? who can let me out of the terrible nightmare. Is there a people the same as me?