I finally gave in and decided to catch up on my RSS feeds, and I came across this article, which quoted author Josh Shenk, reminding me that writing a book-length project is hard:
Writing a book is a crushingly lonely experience in ways that no one who hasn’t been through it can really imagine.
Reading this helped me recognise my restlessness and nervousness of the last few days – I'm at the point in the project that the initial excitement has worn off and I'm far enough off from the end that I'm feeling the burn, it’s getting progressively harder to maintain a good pace. I just have to recognise to myself – yes, this is hard, yes I’m lonely because I have declined all social invitations in order to write, and that’s just how it is. But the good thing I that I'm not the first author to face this, I'm not strange or weird. Knowing others have gone through this, survived and gone on to other projects makes me feel much better.