Sorry you had a bad test day. :(
No, the practice exams aren't designed to give you higher scores than you're really capable of getting. That would leave us with lots of very unhappy customers.
There are several reasons why scores can drop on test day. Timing is probably the most common culprit - it's possible that you have timing problems. (Well, actually, almost everyone does have timing problems to some degree, so you almost certainly do too - but you might have serious timing problems.)
You also mention feeling like verbal was very tough and confusing and you felt drained of energy. That means there was likely a problem with mental stamina. Were you taking your practice tests under 100% official conditions, including essays, length of breaks, etc?
Read this article: when it describes mental fatigue, does any of that sound familiar to you? Did you experience that on test day?
http://www.manhattangmat.com/blog/index ... you-crazy/You mention SC in particular. Over the past year or so, they have been increasing the emphasis on testing meaning as well as grammar (they announced this last fall). Did you study meaning or did you mostly concentrate on grammar? If you weren't adequately prepared for meaning issues, then you likely would've felt like you were sometimes narrowing down to 2 or 3 answers and then couldn't tell what to do from there. Maybe 2 answers both seemed fine (even though they were different).
Also, as a side effect of the meaning issue, a greater proportion of questions now will have longer underlines and will have larger "chunks" of the sentence moving around or changing. Did you feel like this was the case for you? If so, did you have a technique for handling these more complex sentence structures?
Here are some resources on meaning (you can browse our blog for more):
http://www.manhattangmat.com/blog/index ... orrection/http://www.manhattangmat.com/blog/index ... on-part-2/http://www.manhattangmat.com/blog/index ... h-meaning/http://www.manhattangmat.com/blog/index ... problem-2/And here are some resources on long underline / chunks of sentence changing questions:
http://www.beatthegmat.com/mba/2011/03/ ... sc-problemhttp://www.beatthegmat.com/mba/2011/03/ ... -problem-2