i have 2 exams left (one of which will not count towards my UAI) but i find that cramming the night before works despite what teachers and everyone says.
as long as you can fit in 4 hours sleep so youre not totally exhausted, the adrenaline that kicks in is enough to get you through the exam and youll be thanking yourself when youre able to answer a question due to late night study which would have otherwise be spent sleeping. also try recall everythings youve studied once you do go to sleep, keep your mind active and reinforce all your knowledge.