I feel everyone goes through "down time" (including myself), but really don't feel it's a bad thing. I think many times it simply means a person is maturing, and doesn't want to take the same type shots over and over again. So trying something different (even if it's the same type shot) regarding time of day, and type of light might help. When you're making it more of a challenge it might do the trick.
Life events can also play a big part in slacking off, and often when our personal life gets better, so too does inspiration. Or at other times, people use it as an escape from everyday hassle. While I can't offer a cure, maybe look inside and see where the motivation came from to begin with, and you'll understand better why it seems missing now.
One thing I've always found which helps is browsing the internet, and reading articles. Eventually something helps spark a feeling which makes me want to shoot. If not I find I learned new things, or remember things I'd forgotten once the urge returns. There's more to it than just snapping a shutter, and though it comes natural to some... I've never been one of the lucky ones.
Hopefully, whatever it is you'll find an answer soon.