I hate the term "mystery". That's not what I write. I think the Scarpetta novels are much more character-driven than an average puzzle solver. Writing should be like a pane of glass - there's another world on the other side and your vision carries you there, but you're not aware of having passed through a barrier to get there.
But when I was a little kid, I was always writing stories and illustrating little books that I would create.
Even when I am writing I usually take a break around lunchtime and go for a little walk to clear out my head.