From The Children's Book by A.S. Byatt: Her response to any performance, any work of art, was the desire to make another, to make her own.
This is my response, too, when I do any of the above. If I'm away from home, I scribble the idea into a little notebook I carry just for that purpose. If I don't act on it soon, though, it's birth and death will be in that notebook.
When I think about all the art I could have made, all the stories or songs I could have written if only I had taken the time to act on an idea, it makes me sad.
But instead of dwelling in sadness (which isn't very conducive to making art) I'll try and put that attitude away and focus instead on what I have made. Better yet, I'll plan in my head the things I'll hopefully get around to making soon.