Start listening to bands you've never listened to before, try out different techniques, and play play play.
Whenever I hit a roadblock in my playing, I usually just dive in even further and smash right through it. Either that, or maybe try getting a small piece of gear to revive your enthusiasm for playing.
Recently I was feeling kinda down about my playing, really stagnant and just kinda bored in general, PLUS my band was dissolving after like 9 years of playing together, which didn't help matters. Then, for no real reason at all, I picked up a pair of used MIM Fender jazz pickups here in the classifieds for $30 to put into my $250 Peavey Millenium BXP bass that I never even used.... and wow! It was hard to imagine such a small (and cheap!) change would make such a huge difference...
Long story short, the gnarlyness of the new pickups brought out something that totally fired me up for playing bass again. When I combined that with a heavy dose of Rush 2-3 times daily, BAM! problem solved. Not only did I feel amazing about playing bass again, but I was actually playing better than before! I actually used that bass over my $2000 Yamaha for my band's final show ever this last weekend, and wow again! Not only did it sound great, but I think it brought out some of the best playing of my life. I had people I've never even met before beg me to not quit playing after our set.
So, my advice if you're feeling down would be to pick up a new toy... doesn't need to be expensive or fancy, but as long as it makes you feel better about your playing, that could be all you need.