Yep, it happens to all of us. One thing that helps, but may not be that practical, is having an upcoming gig. I don't gig that often, so when I do, it tends to keep me focused and interested. Truth is, sometimes you just have to walk away from it for a while. When that happens to me, I often try to focus on playing something completely different than what I've been working on. I play a little mandolin, and that's a great way to change your musical mindset for awhile. Try grabbing your acoustic, if you have one, and playing some old folky stuff, teach yourself to fingerpick, play slide.