For now it is necessary to contemplate just how different the interpretations for both of these types of doppelgangers would be and what it would means to dream of each of these symbols.
If you have a dream about a doppelganger or a dream where you see your own doppelganger then this means that you do not feel unique anymore. A doppelganger can mean one of two things, it can mean that there is a person who looks quite a lot like you but is not you, and you see them walking around near you. A doppelganger can also mean an exact copy of you though in practice this cannot actually happen, this would be associated with the supernatural. Of course if human cloning were legal you could have a real doppelganger but then this might be referred to as a clone. Regardless though, the meanings of the dreams are essentially the same as far as interpretation is concerned. A dream of a doppelganger means that you feel as if your personality has been encroached upon and you no longer feel like a unique human being. You feel copied.
While this thought is common and even something that just about everyone feels at some point in their lives, it is not anywhere near healthy and if you start to have these kinds of dreams it may be best to try and find something unique about yourself and latch onto it. You need to cling to the perception of your own uniqueness or you will end up hurting yourself mentally.