This happens to me once in a while, and though I can go on for days without practicing, I eventually get back to it at some point. The mistake I keep doing is, I practice more than actually play the music for enjoyment or thought articulation, and this seems to serve neither. Listen to your classics over again, get re-inspired by them, think of them primarily as music, secondarily as piano music. Problem I've found after I started playing piano is that whenever I hear a piece I'm practicing, I imagine the fingers playing it, and it sometimes blurs the actual music.