Hallucinating Music by Memory

Sometimes, when we like a piece music so much, we can sort of hear it in our head even without playing it on a media, on Youtube, CD, DVD, or BluRay.

This takes place a lot throughout the day, but when it happens at bedtime, it can be annoying - forgotten words, forgotten melodies, or simply just repeating over and over in our heads. It might be considered obsession, but we sort of have to be able to do it on any piece of music we are studying.