I'd call it a bit of bad timing, but when you've got deadlines, it's all bad timing. I'm in the middle of my WIP, which means for me that I have about a quarter of the novel written, out of order, with a lot of scaffolding with notes about what else may happen. Things will start to really take off with the next fifty pages or so, and work will progress faster until I reach the three-quarters point, and then I'll stall for a bit, then finish the book at a feverish pace.
I know this will happen because it's happened on seven other novels and sixteen short stories. I kept notes, the first few books I wrote, because I needed to learn whether this was just my process. It happens every single time.
The dread of hitting the middle is huge. Doubt floods my mind and worry nibbles at my nerves. The inevitability of it is rather like a horror story. You know the process, can see it's happening, but refuse to think it will be as awful this time, until it actually is. No, they're just freckles, you tell yourself, in denial as the tentacles start to sprout. The alien didn't really bite me, I'll be just fine—gaah blorgel Earthlings, gaah blorgel!
I do not exaggerate. Horror.
Ordinarily I'd switch over to my Plan B—another WIP in a different style, voice, etc. That let's me leave a problem, focus on something else, and gives my brain to figure out the next step in Plan A.
The thing is, I'm in the middles of Plan B and Plan C as well, and I can see the little suction cups starting to grow on the tentacles...
These are things I do. I keep at them (or variations of them) until something gives.
Change the music. The playlists I use can create a groove—or they can create a rut. Sometimes I have to find a different style of music to shape my POV.
Change your space. If you write in the kitchen, move to the living room. Switch coffee joints. Painting your office might not be an option, but maybe changing your pictures around, or adding new ones, or taking them down entirely is. I put up some new art, and even if it changes the way I feel for just a second, it's useful. The picture (above) is the first thing I see when I enter my office. The calligraphy translates as "narrative."
Read/watch something you ordinarily wouldn't read/watch. Sometimes that will give you a different perspective on where you're stuck. If you're curious about fashion design or physics or monster trucks, chances are there'll be something there that speaks to you about your current work, however indirectly.
Discuss the problem with your character. For example, “Dear X, you really are stupid today,” oftentimes X will answer back. “Well, if I am stupid, it's because you had me use the same solution to the last two problems, and I'm cleverer than that.” Surprising how often that works.
Don't discount the thoughts you've already had. This is a new one for me and it's important. I have a list of things from Pack of Strays (out April 15, and available for preorder today!) to address in my next Fangborn book on my whiteboard. You'd think I could go through, do them, cross them off. Dust off my hands and call it a good week's work. But for some reason, I think “oh, but I've already had that thought, it doesn't count. I need to have a new thought.” No, it doesn't count because you haven't written it down. Those loose thoughts in your head? They belong on the page. Write them down, however imperfectly.
Finally, if Mal's motto in "Firefly" is “keep flying,” ours must be “keep writing.” If the middle is inevitable, then the solution is too.