a great piece of advice I got was to pick a time the night before the test and NO MATTER WHAT, stop reviewing / studying / freaking out at that time. I chose 9pm, and mostly worked on memorizing PS formulas and scanning Bio. when the time came around, I felt anxious about stopping (there's so much more I could do!!) but as soon at 9:00pm hit, I felt a huge weight lifted off my shoulders. I knew I had put the time in, I felt relaxed and confident, and that feeling carried into the next day. I also got a great night's sleep.