I've been there, I view it as a motivation problem.
1) I'd definitely advocate exercise, nutrition and a break from the "mundane-ness" of your day-to-day grind.
2) Taking a scenic vacation would also be ideal.
3) Focusing on other pursuits (i.e. building a side-project, teaching your kids something new, etc.) will also give your brain the ability to recover quickly.
Often, I feel like burnout is inevitable but you can limit the refractory period if you're disciplined.