I stop doing work on nights & weekends. I generally very much enjoy my job, but when I start to feel off, I cut off all work and just focus on other things that I enjoy. I read more, I play video games, knowing they are "pointless, and I should be using my time better". I watch a movie with my wife instead of opening the laptop and working.

I've found this works fairly well. Sometimes I'll go for two weeks or two months of just turning off 'work'. It has the advantage of letting me continue to be employed.

One of these stints was also when I thought hell, why not try and learn Haskell? ;)