For those who have only recently started reading this blog, I will reiterate the method I used to do well in grad school and graduate as soon as possible: don't do any work between 8 pm on Fridays and 1 pm on Sundays. Friday and Saturday nights should be reserved for partying, while Saturday afternoons and Sunday mornings are for reading for fun, snoozing in front of the TV, or pursuing any non academic hobbies you might have. I broke this rule only once, which resulted in the crappiest final essay I have ever produced. After that, I learned my lesson and stopped sacrificing my free time to appeasing my misplaced feelings of guilt about not being "productive" all the time.
Whenever I shared this strategy with my colleagues in grad school, I always heard strings of dire predictions about how I would never be able to graduate. Curiously, I was the first among my entire cohort to graduate. Actually, nobody ever graduates in 5 years from my program, which is something I did. Burnout is your enemy, my friends. Don't let it take over your life. Intellectually, you will be useless unless you are well-rested.