I started a new manuscript recently and the first week of writing went really well. Instead of daily word count goals like many authors have, I set weekly goals for myself. This week I won't make my goal because I've been sick, and for a change, I'm not stressing over something like that.
In the past I've pushed myself and treated writing a novel like running a race. But it's really more like a marathon, and more than one kind of pacing is important. Pushing yourself to create the best work you can is one thing. Pushing yourself into exhaustion isn't necessary to writing a good book. Sometimes you have to take a day off, or settle for just a few hundred words. I know this winter sinus crud that's attacking me won't stay forever (I hope!) and when I'm feeling better, I may even catch up on word count and be where I'd wanted to be in the wip. Or I might stay behind, and that's okay, too. I have a deadline for this book, but I made sure to give myself plenty of time when I offered a time frame for it. It might be tempting to say, I can do it in three months easy peasy. But stuff happens. Life happens. You get sick, your toddler won't play by herself, the kitchen floods. Anything can happen.
What I'm trying to say is this: cut yourself some slack. Know when not to write, and go play with your kid or get yourself healthy or whatever you might need to do. Accept that not every day will see two thousand words added to your word count. Give yourself plenty of time when committing to a deadline. Give a book the time it needs, even if that's longer than you might like. It'll be worth it in the end.