I notice that often right after waking up, in the half-asleep, half-awake state, a song usually starts playing in my head. It also plays in my head most of the morning after. This happens nearly every time I have a deep dream, now that I think about it . This happens so much I don't think twice about it, or I'm already tired anyway that I don't think much on it. For me, the song that plays really sets the mood of the dream. Like my mind wanted to come up with a song to leave the feeling of my dream with, like in movie credits. It's so strange, but it does make me feel better. This morning was, "Don't Let the Sun Go Down on Me," lol. I hadn't heard that song in forever until it popped into my head this morning.