Motivation - Getting the Spark

I've been having some difficulty motivating myself lately. And I really can't pinpoint it to something that is causing this. I have no complaints about how life is treating me, I'm healthy, have good kids, great friends, nice place to live, good job. But I have this general malaise that has crept in and I can't seem to shake it. And I'm usually pretty good at shaking it off. And that probably has me worried more than anything. Rather than coming out of this I'm in a holding pattern. I need to find that spark. But where?