Same here, I find the best thing to do is just "vegitate" or rather don't even approach anything about the prject or related for a day or two (In extreame cases a week or a month). Distract youself with a new movie or something too, nothing mindblowing just something stupid you know will be bad but your brain doesn't care (Last time it happended to me it was Undead or Alive but that movie was so bad it didin't help.
