ChemJobber is starting a series of posts today on grad school and its effects on the mental health of grad students. I have to say, the story he relates sounds very similar to some of my own experiences during my third year or so. I didn't break any household items, but I recall (for example) several instances of leaving the lab and getting back into my car late at night, but first pausing to shout a lot of foul language at the top of my lungs while beating on the steering wheel.
I really did have some moments where I wondered if I had made the mistake of my life, whether I was any good at all in my chosen field, and so on. Another big worry was that I was, from what I could see, losing my ability to enjoy what I was doing, and I had a great deal of worry about whether it would ever come back. (It did, by the way, but I had no way of being sure about that at the time). One of the biggest factors, I think, was the day-night-weekend-holiday nature of the work. My brain has a lot of things it enjoys doing, and being chained to the same wheel for an extended period doesn't help it any. Being persistent on my own motivation is one thing, but forced persistence is another thing entirely. I ended up (as do many grad students) worrying about every break I took from the lab. I'd go see a movie on Saturday night, and come out thinking "Well, there's another two hours added to my PhD"), which isn't a recipe for fun.
There were other stress factors, and looking back, it's a good thing that I started being able to deal with things when I did. The push I made in my fourth year to get things finished up was not without its problems - there's one story that I was sure I had told here before, where I inadvertently destroyed the largest amount of starting material I'd ever made, but I can't seem to find it in the archives. If I'd done that during one of my lowest points, I'm not sure what I would have done. But by that time, I could see the finish line, and I was devoting all my effort to getting out as soon as possible, having decided (correctly, I've always thought since) that doing so was the single biggest thing I could do for my career and for my sanity.
Having that as a goal was important. 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. I think that everyone who's been in a graduate program in the sciences will have seen similar cases. I became determined not to end up as one of them.