Dont worry Buddy,
I took my GMAT recently and got a shock too.I ended up with a 640.
I had also been scoring in the 680-720 range in the practise tests.
Take a couple of days off.Let things fall into perspective and then start again.
I cleared my head off for a couple of days.Just gives you a better perspective on where you went wrong.I second Kz regarding reading Wall street Journal and stuff.
Also, do small but timed sectional exercises for verbal.1000 SC is a good source.......