There are times when everyone gets burnt out. Yes even in writing. When words seem to come get you instead of singing sweet songs in your ears. It's not writers block but something more, as if the fire of writing has left ash in its wake. As the forest fires of nature, seeds are left under the grey dust, but only time will bring forth the sprouts of new words, new ideas, and reinforce thoughts to old ones.
Everyone gets burnt out at some point. Thinking too much on a Manuscript, revising and rewording over and over. The words get jumbled together. Thoughts fade in the mind before they get on page.
The only cure is time. This is why it is not always good to write every day. Rest from the words, read a book, or if that is also too much, play a game, watch a few movies. Take a week or two off to refresh your mind. Do anything else. I would suggest not even thinking about the MS, but I can't even succeed in doing that, so I wont push the thought.
Writing has it's own stamina. You may not use physical energy to do it, but there is energy spent every time you jot down a word. Don't be surprised when it hits you. When your mind feels like a ball of lead, unable to absorb or put forth the words that create your elation. Just back off, let time rejuvenate you and you will find the words flowing again, the ideas bouncing around just begging to escape.