Is this short term burnout or long term? Meaning is this a few days or weeks of a tough project or are you questioning the entire job/career?

If it's the former, Gus has good advice each day. I'd take a couple walks a day, just get away from the office. I'd also say that you ought to work less hours. No matter what, going over 40 is going to make you much, much, less productive.

At the same time, I'd say when you sit down in front of the computer, double down and focus on what needs to be done, not what you want to do, and work on it, with the idea that in 90 minutes, you'll stand up and move away for 15 minutes.

If it's long term, sit down with your mentors, your family, the people that matter in your life and do serious soul searching. Think about what is really important to you. Then build a "get there from here" plan. Sometimes adjusting your attitude, or seeing and end to the current situation can help you.