Do you have to play this for an audition of in a performance?
i.e. is there external pressure or just self-imposed pressure?
either case, go play something else for a while, something harder, something easier, something new, something old, doesn't matter.
when you start to get tired of this alternate piece and just about used up your practice time, go back to the piece in question and just play it through maybe 2 or 3 times and no more.