I had never heard of maladaptive daydreaming until now and I'm no doctor but that doesn't sound like a bad thing at all to me. I sometimes do the same thing with the pacing and the pretending to be a musical genius. I even take it one step further sometimes by picking up a marker and pretending it's a microphone while I lip sync alone in my room, pretending I'm on stage and everyone loves me. I'm 25 and I'm still doing that kind of thing, I've been doing it for years! It is therapeutic! And totally embarrassing. But I don't think it's unhealthy. However if this is something that you feel is unsettling than I don't see any reason why you shouldn't tell your therapist.