Hi Praveen,
Test Day is a rather specific 'event' - the details are specific and they matter, so you have to train as best as you can for all of them. The more realistic you can make your CATs, the more likely the score results are to be accurate. The more you deviate, the more "inflated" your practice scores can become - and that's what happened here. It's not clear what you mean when you say for "most" of the Exams you took the full Exam, but if you ever skipped sections, then those score results are likely 'inflated.' In addition, by taking the CATs at home - along with any of the other details that did not match what you experienced on Test Day - you weren't properly training for the FULL GMAT 'experience.' Having to rush through the last 7 Verbal questions on Test Day could have certainly hurt your score (especially if you got them all wrong), but it would not have been enough to turn a V37 into a V21. This is meant to say that you were 'in trouble' in the Verbal section far before you neared the end of the Exam. From what you described, there's also a question as to how 'hydrated' you were on Test Day; if all you consumed during your two breaks was a banana, then you might have been suffering from some mild dehydration - and that could have also impacted your performance (especially later on in the Exam).
1) Have you purchased the Enhanced Score Report for your Test? While the ESR doesn't include much information, the data in it usually points to a few specific areas that you will need to work on to improve. If you purchase the ESR, then I'll be happy to analyze it for you.
Thankfully, the GMAT is a consistent, predicable Exam, so you CAN train to score at a high level. Given this recent score result though, you have to be mindful that "your way" of approaching this process might continue to earn you a similar score.
GMAT assassins aren't born, they're made,
Rich