Hey, it happended to me also. I took a weekend off ( generally weekends for me are the most productive in terms of studying) and went on for a movie, shopping, eating out with my wife and by Monday i was feeling lot better. I have done like this on couple of weekends, once every month
I wont suggest you to take a week off or so as your date is nearer, what you can do is take couple of days off and restart. You will feel rejuvenated. Take a break, watch some cool movies, hang out with your friends ( which you have already missed a lot due to GMAT prep) , go for the near by pub and have a drink (not much
) ; Just chill out for a day or two and you should be fine.