So, you joined NaNoWriMo this year with the intent of finally getting that novel out of your head and onto the page. Odds are your started out really good, but after a week or two, things started to slow down. By the end, you hadn't written on it for days and what you did write is pretty much gibberish.
Don't sweat it. Only a small fraction of people that join NaNoWriMo actually get through to the very end and frankly, that's a good thing. If everyone that joined actually wrote a book, then the market would be flooded with thousands of hastily made books self-published and sitting lonely on Amazon's digital shelf.
NaNoWriMo isn't actually about writing an entire book, it's simply a way to spur creative thinking and writing. If you get through half your book, then you're half way to finishing it. Don't think of the end of NaNoWriMo as a failure, but as a success. If you even wrote one additional word on your novel, then you did what you were supposed to do.
The key to getting the most of NaNoWriMo is to take what you've got and make it better. NaNoWriMo is supposed to be about regurgitation. It's literal vomit. You puke it out and then it's up to you to clean it up. Now that you have something written, take it and polish it. It might just spur you on to more writing. I know it does for me every year.