Man the best advice you'll get on this issue is to just relax and trust yourself. I do the same thing when I study and practice non stop. You get to where you're subconsciously saying "I know I'm good on this type of question" and so you don't give it the full effort it requires and it tricks you. You won't even realize you're doing it most of the time. So just give yourself some time off maybe a week, I don't know when you are taking your test, and then come back to it fresh and make sure you take your time on each question and I promise you will see your scores go back up. Hope this helps.