Went from 3 consistent 700+ practice tests to 640. What can I do?

Dear okavishi,
I'm happy to respond.

My friend, students sometimes imagine that their "GMAT level" is a fixed quantity, like how much one can bench-press. Yes, it takes time to build up, but once you have it, you should always have it. That's what people think, and it's not really true. You see, performing well on the GMAT requires you to be in tip-top shape in all ways. If you are tired or haven't eaten well or are stressed in any way, that could have a huge impact on your score. This is precisely why only 10% of the test taking population gets above 700. Probably twice as many have the knowledge required to get over a 700, but to have everything "lined up" in one's metabolism and psyche so that one is operating in peak form is very hard.

The good news is that you can do this. You have the intellectual talent to cross the 700 barrier. Now, you just have to get your body in top form so it can support your brain.

Here's what I'll suggest over the next few days:
1) every night, get fully adequate sleep, even more if possible. If you can take a day off and sleep late the day before, that's ideal.
2) eat very well between now and the test: no junk food at all, only high quality healthy food.
3) drink a lot of water
4) no soda, no alcohol, no drug
5) practice slow deep breathing, full belly breaths, constantly throughout the entire day
6) keep your mood positive: deeply confident and without any attachment to outcome

For more, see this blog:
Zen Boot Camp for the GMAT

Let me know if you have any questions. Best of luck to you!

Mike