TL;DR I experienced massive burnout after ridiculous working hours and a broken contract
I experienced terrible burnout around a year ago that I'm still working to get over.
I had taken a pay cut to join a startup with the promise (contractually) that I receive a raise to market value + bonus after 12 months. The latter 6 of those months were spent working 16 hour days ramping up to a massive launch. There were multiple times were I was in the office for 40 hours straight. Throughout this entire period I was locked in and producing top quality code.
A few months after launch I approached my boss about the contractual raise + bonus. After blowing me off for a few weeks I had a meeting with the president and CEO where I was told that I would not be receiving either because I was not coming into the office by 10 AM. Not only that, but they told me they didn't appreciate the amount of work I put in, nor the fact that I had barely seen my family and friends in that the period because "no one asked you to do that." Mind you, our CTO had quit with 4 months to go until launch so I had taken some of his responsibilities, and I was the sole developer on Android, and one of two for the backend. All the while the feature requests kept pouring in.
Within a week I was bedridden, and I stayed that way for the next 3 months. I've been slowly recovering since then, but I'm not sure I'll ever be the same again.
I know I could've sued for the money, but it was the lack of even a basic appreciation that did me in.
Some people have told me that I have no one to blame but myself. I sort of agree with them, however, I know that if I would've gotten my raise and bonus I would've been fine.