passed first time, never tried though.
the way I see it, you can stay up all night confusing your brain revising, come in tired, do more revision being tense and nervous and make mistakes. Or you can get an earlyish night, wake up as late as possible in the day but way before exams, have a shower, have some brekky. Then go do the exam, nice and relaxed, not worried, not stressed out through revision, relaxed and ready to pass.
i remember one of my a levels, i was sat at the nearby pub in the afternoon have a drink, reading my book about keith moon, oh, i've got an exam in 20 minutes. Finished my pint and took a slow walk to the college.
I got full marks.