Is the next chapter jelling well?
Have you run out of ideas?
Does the prose sound stilted and boring?
Or is it simply TAKING TOO LONG?
Although all of the above is part of the process, sometimes a tired brain needs a pick-me-up and an encouraging pat.
So while you're brewing another cup of dark roast, open up a previous chapter (or essay, poem, etc.) and not a recent chapter either. Pick one that felt laborious to write at the time, one you meticulously self-edited.
Read how nicely the words flow. Feel the joy in reading it. Remember the long journey to get there.
See? You can do it. You can really, really do it.
You just need time.
And more hard work.
The Holy Trinity of good writing. Amen?