Your physical conditions matter a great deal too. Make sure you get enough sleep, eat well, and exercise. I've never tried it personally, but some people on this forum are recommending regular meditation too.
One thing that's worked quite well for me has been mindfulness meditation before taking a practice test. It sounds like you're pretty stressed out... that cumulative stress can cloud your thinking as you go through the test.
@"Cant Get Right" said:
So, up at 6, shower and all that, breakfast, coffee. A few random games, a LR section or two, then some green tea and relaxation (My version of meditation).