I saw several examples of grad students who got trapped at some point in their work or their writing-up phase, and were having a lot of trouble actually moving on to something else. Staying where they were was causing them damage, but they seemed to feel even worse when they tried to do something about it. Some of these people eventually pulled themselves up, but not all of them, by any means.
Yup. I was that. One of the greatest and worst experiences of my life. I still have nightmares.