I'm not sure I'm ever uninspired. I might not always be as proficient as I'd like to be, but the desire to write is almost always there.
When my mind wanders, or when my muse resists, it's usually because I have a story glitch to fix, or maybe I hadn't given enough thought to an upcoming scene. Or a scene takes an unexpected turn...
That's when I have to walk away and think things through.
I'm not what many would call a "plotter". I'm not a pantser either. I do plan my stories, and I do lay out scene progressions, but not in detail. That limited bit of planning works for me. Uncovering certain details as I write is the best part of the work.
When the details I uncover threaten to take the story in a different direction, the pantser part of me is always eager to explore that new option. The plotter in me resists, aware there was a plan to follow - loose though it might have been.
This is the tough part of the job. Do you follow this new lead or stick with the plan? Which will make for a stronger, more satisfying story?
I suppose the inspiration to write comes with the answer to those questions. Because when the answer is there - just beyond that fog of words yet unwritten - the inspiration to write is at its peak and impossible to resist.