I don't know about you, but I find I frequently have this problem. I'm settling down to bed, about to start working, or heck even driving and this lightning flash of inspiration hits me. It seems it's never at a good time either. When I should be doing something else or focusing my attention elsewhere.
For several years though I was out of touch with this flash, my muse I'll call it. Why she left me, what indiscretion I performed to offend and cause her to leave I don't know. I have to say it distressed me greatly as I don't believe in forcing inspiration or art.
But as before (when I was in high school and had my muse speak to me almost daily) I am struck often by the quiet whispering of ideas. While the end result is much more on the physically creative side these days rather than writing creation is still creation.
So what inspires you? Is there some invisible unseen force that pulls & directs you? Are you inspired by things you see?