One such realm concerns the involuntary and spontaneous intrusion of musical tunes in one's head. The phenomenon is called "earworms." Although these are not unnecessarily unpleasant or worrying, they typically are hard to control, meaning that one can neither stop nor start them.
I have had such earworms ever since I can remember. I experience music in my head from the moment I wake up until the minute I fall asleep. Where the melodies arise from I cannot say. They bear no relationship to music I have recently heard, and they typically consist of advertising jingles, popular songs, and excerpts of classical music and opera. Decades ago when Sony first introduced the Walkman I marveled as everyone else did at the fidelity of its sound. I did not buy one, however, because I could voluntarily "play" any song I chose in my head. To me doing so didn't sound any different from the actual recording. At the time I still engaged in cross-country running. To pace myself I usually played Howard Hanson's Symphony No. 2 in my head. The last moment has a strong beat sounded out by the tympani.