You said "when it comes, it's a gift" and "it waits until you least expect it" about music (and humor).  I often have this feeling, and I even have good ways to catch the "seed of the gift" by writing it down or by recording myself singing/playing, accurately enough to be able to reconstruct it.  However, I can reconstruct the music but not the feeling/vibe/enthusiasm and it seems dull afterwards and I give up. It seems that a good solution is to continue no matter what (not expecting to be fed by the "good feeling" while working on it),
sometimes yes