Shaken by the GMAT!

I'm sorry to hear that you scored was below your expectation. I had a similar experience 6 months back when I took my GMAT and scored 680. My test scores ranged from 660 to 750 and the actual test seemed to go smoothly with only a few difficult questions. I was confident in scoring above 700 but that was not meant to be. What threw me off was my verbal score. I consistently scored above 42 in all my practice tests but scored only a 36 on the actual test.

Just like you, I was also confused about what happened. However, after some introspection, I realized that my verbal skills, though strong, did have a few weaknesses.
I concluded that since this is a percentile based score, others who took the GMAT probably made fewer mistakes than I did.

Your average practice test score is around 700 which, +- 30 is where your actual test score lie. So while you scored good on certain practice tests, maybe you did so because those verbal questions tested your strong skills rather than the weaker ones. You'd probably want to do an in-depth analysis on your past verbal questions and the skills tested there to see if you can find a pattern or isolate weaker areas.

From what I have read and understood, a few wrong answers in verbal can result in a larger score difference on verbal than on quants.

then again, I am not an expert. I hope some of the GMAT experts can give a more scientific explanation.

Either ways, hope you try again and good luck!