system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does a song sound completely different after listening to it while asleep?

I fell asleep last night listening to David Bowie's "Life on Mars" on repeat. Today I went to listen to the song and I didn't even recognize it, I thought Spotify was messed up so I tried YouTube and it was the same. Then I used the same headphones I was wearing before and it still sounded wrong, just something was way off. I googled around and found some other people who had experienced the same thing. What causes this, and will it ever go away? That was my favorite song of his and now I can barely listen to it.

Edit: Just to clarify what off about it, the piano seems louder even though I had never really noticed it and his voice seems to be deeper and slower tempo. The intro of the song is almost completely unrecognizable besides the lyrics.
gpt
During REM (Rapid Eye Movement) sleep, the brain activity fluctuates & changes very rapidly and processes the music constantly. The sound of the music will get so familiar, after listening to the same song for several hours on a constant loop, the brain anticipates what will happen in the song. So basically, you know when a riff is coming, or when a tone will pitch. In other words, you get bored with a song eventually.