Slump-ish-ness

    
     Does anyone else go through the mid-book slump? This is actually the first time I'm experiencing this particular problem. I'm 40,000 words in. I know exactly where my WIP is going. I know what's going to happen next. I'm not having problems with plotting. I know how the story ends. But for some reason, I've lost that manic enthusiasm I had in the beginning. I wonder why. I feel like I'm dragging and therefore it feels like the story is dragging. Not good.
     So how do you get that enthusiasm back? What do you do?
     I know some people just put the story aside, even for a little bit, and work on something else. I'm way too neurotic to do that. I have to finish this. But how can I get excited again? Because I feel like when I'm not fired up, it reflects in my writing. I don't like that. I need it back. I need my writing mojo back.
     Any suggestions?