Okay, where do I start?

I've been coming up with random songs in my head, lyrics, music, full-blown, SONGS. I don't get it, if I don't have any music I feel like listening to, I just randomly come up with something for no good reason. Did I listen to a song that sounds similar to it? I don't know.

Then sometimes my mind just works as a mp3 player and I just randomly pick a song of my choice. My friends keep getting so annoyed with this song stuck in their head and I'm just here listening to Promise (EXO) in my head before switching to Taeyeon's I.

I don't get any of this, like I don't get how my friend can read on the bus with no motion sickness. I might as well stick to my first theory for now.