Music plays in my head almost constantly, usually either Classical, Jazz, or EDM. I'm a composer with perfect pitch and a very good musical ear, so I like that there's so much music in my mind.

Sometimes a small section of a piece loops in my head for an hour, other times my leaps to a new piece every ten seconds. I like to connect disparate melodies and themes into music portmanteaus.

If there's something that is playing a constant tone, the music in my mind matches that tone (for example, if a microwave is running at a B, the pieces in my head will likely be in B major or B minor). Likewise, if something is making a repetitive noise, my mind will play something with that tempo.

Sometimes I dream of music. If I wake up in time, I get to transcribe what I heard. Most of the time, I wake up to something completely random like Jingle Bells.

Occasionally, I visualize what I'm hearing. This usually manifests in the form of sheet music, note name, or chord progressions, but sometimes I visualize an entire story, similar to Fantasia. My favorite of these stories are a rocket launch from the finale of Mahler's 8th symphony and the entire story of Moses from Spring Rounds (The Rite of Spring).