Well, I'm not really a writer but I try to do the Nanowrimo every year (and usually fail because I let life get in the way)
This year, 48 hours before the deadline I was 10 000 words short.
Started writing around 1 AM, thought I'd just write a few sentences that I would use as a prompt the next day... Only got to bed after writing something like 4 500 words, it was just flowing. Next morning first thing I did after waking up was going back to it, I had so many ideas and then again, it required no effort, it all made sense and every loose end in my plot got tied together like magic, I had so many things to say and the words just came right (probably way better than that very sentence I just wrote but it's 1:30AM and I'm French and tired so I'll leave it as is).

So long story short, on the last day I needed something like 1000 words to complete the challenge... Took me all the fucking day and it's probably the worst part of my novel.

TL;DR: I can write between 9000 and 1000 words a day and I have no clue how it works.