I think the trick isn't so much in the down time (or the length of it)...it's in what you do with any free time.

Burnout is generally a result of getting stuck doing lots of stuff you don't want to the majority of your time...and generally very little of what you do want to be doing...

So in my experience you only get over burnout by focusing and rediscovering what you were truly passionate about in the first place (or at the very least what you are insanely passionate about now).

Then, once you can figure out what excites you, start getting small wins in that direction however you can...and before you know it, you'll be full of energy and near impossible to stop again.