The simple thing to do is take a break, wait for a flash of inspiration, plan your next phases of writing and then go at it again. Writing involves discipline, therefore if you want to complete your book you've got to keep on writing until the bitter end. Just give yourself the space and time to recoup if you overdo it.
I wrote my first 30,000 words within one single month. 1,000 words a day throughout June. I then got writers block and didn't start writing again until a holiday the following November, where I knocked a further 25,000 words out within a week.
My next book, out on Kindle soon, is going to be about my experience of writing and how you can get over things blocks like this.