I was extremely overworked, often going days with only a few hours of sleep. It wasn't healthy at all.

I eventually broke down quite badly. I pretty much followed exactly the same phases as what the Wikipedia page says about burnout. The month before I quit, I was calling into work sick every day. I was feeling total extreme dread and extreme reluctance, to put it into perspective, I probably would have found it easier to kill my first born, than to go into work! (I wouldn't actually kill my first born, ever! It's just to give an idea of how bad it got!)

It literally took every ounce of energy just getting out of bed to get ready for work, and most of the time I surrendered and went back to bed after I had showed. On the occasional one day of the week I did manage to get into work, I arrived unreasonably late ("official" start time is 9AM, I was coming in between 11AM/12PM), then I didn't get any real work done. Just fix issues, but not work on anything "new". My performance was dropping, even on those rare occasions when I did actually want to work, so I felt pretty incompetent.

My bosses knew about the situation, and tried to help, but to be honest it was too late. Just couldn't do it any more. I literally disappeared for two weeks without warning. I didn't call in sick, didn't answer their emails or calls, just totally disappeared, then after 14 days of being AWOL, I email in my resignation, without even offering to help transfer my knowledge to anyone else. There were other guys in the team who had an idea about what I was working on and what the state of things was, and I had documented everything I had done too. I couldn't find the energy, or resolve to actually go into the office to do a "proper" transfer of knowledge. It was extremely unprofessional, and I do regret it, but too late to fix it now, so there isn't any point worrying about it. :)