I actually did the same thing for the same reason, with MIT. I guess it depends on the department, but the department I am going into was very happy I took the time off to have more energy to start school. Definitely worth it for me.
And yes, it took a full year to basically recover from my job. It worked. If you need it, talk to your department, and find out if they are okay with it. Life is so much better with more energy and motivation.