Sometimes I'll not be able to fall asleep with patterns running through my head. I'm in a block swap and if I spent much time looking through quilters cache ... I'll have "block brain" by the end of the night with squares and triangles fighting for competition with slumber!! These are unproductive unconscious images, nothing of substance worth retaining.
Sometimes it will just be ideas ... especially quilting motifs. Came up with a doozy the other night and remembered it and it was just the ticket for that quilt. These are productive unconscious images - and I do usually retain them in the morning.