It's a very interesting thing, music in a dream. I have on more than one occasion dreamed a fully orchestrated piece of music that I had never heard in my waking state. I can remember the emotional impact and I was composing this music in my dream but the music was gone after I awoke.
I sometimes think that if i could tap into the right side of my brain, I could heard and play any instrument or write any thing that floats through my head.
The songs that my wife and I believe are our better work, seem to come with less effort, almost like picking a plum from a tree in a dream. The other songs a labored and are not satisfying till much later when half forgotten we bring them back and rework them with less effort but more creativity, then they work well.
The kicker to all this is I know the music in my head but have yet to be able to play any instrument of any kind, total dyslexia. My wife has to read my mind and to translate non musical terms into rhythm and chords, which she has learned to do quiet well, considering the impossible task I ask of her.
Any time that we create any music is when we have time outside of the noise of life, that noise kills any music that wants to come out.
BTW I'm not saying that what we write is great but that it expresses what we believe and feel deeply about, it may in fact be an illusion in our minds as well.
Just my POV on a very interesting and strange subject. Wyndham