As a supervisor I see a lot of students struggling to get their thesis done in time. It seems to mostly be the other things going on in their life that are preventing them working on it. As a result I find myself generally trying to encourage students to work on their research more rather than less!
But sometimes you do need a break. As Rachna Jain explains in this post, you just get tired and you need to mentally escape from your dissertation. http://completeyourdissertation.com/blog/307/sometimes-you-just-need-a-break/