I dreamed that other students made the music teacher angry and cried. I giggled beside me, and then I was named by the teacher to stay at school for music appreciation at night.

When I sleep, I hear a sound similar to music, which is a sad tune. So you have two associations, one is that music reminds you of music teachers and music classes, and the other is that sad style reminds you of crying. At the same time, your facial expression has changed. You look like crying and laughing.

The brain synthesizes the above information: music+teacher+crying+laughing. Add some characters and plots, and you have this dream.