Relaunching a career

This came up over on the "Burning Management / Career questions" topic that was started for future podcasts and I thought I'd post it here to get some feedback.

I was a rather high performer throughout my 20's and early 30's, experiencing consistent promotions and respect from my peers. But something has happened over the past few years, I've lost the "mojo" that I once had and my performance isn't up to par with previous results. I can't put my finger on what it is, but I can feel the change and my performance reviews are noting it as well; I've essentially gone from the 20% to solidly in the middle of the middle 70%.

Has anyone gone through this and/or  have any advice for resources or self inspection that I can go through to attempt to figure out what's going and hopefully re-ignite my performance and motivation?