When you wake up, your dream continues with your alternate self, the other parallel copy of you. A dream is a scene from an alternate dimension in which a parallel copy of you exists. When you dream, your current consciousness is temporarily transferred to your alternate self that exists in that alternate dimension.
When your consciousness is transferred there, you don't necessarily overlap your alternate consciousness. So, two consciousnesses, and may be more, exist in one body. The same happens in reverse in the current dimension where other alternate consciousnesses of you travel through Quantum level to temporarily merge with your current consciousness, see, experience and react with a specific scene from this reality.