Hi iPen,
The definition of a 'hard' question is something of a debatable subject. For example, you could very easily come across a question in these Forums that YOU think is 'easy', but that other users (or the GMAT Algorithm) would rank as "hard." In that same way, some of the wordiest questions that you'll face in the Quant section are NOT actually all that difficult to answer - they just take more time than average to solve. Does that make those questions "hard" or is that really just a stress-reaction to the length of the prompt and the work involved?
To address your immediate concern - NO, you will not receive an escalating series of questions that become more and more difficult to answer until it is simply impossible to finish the section on time. If you're performing well though, you will almost certainly see some questions that are rather difficult overall (but it will be a relatively small number of the 37 total questions in Quant and 41 total questions in Verbal).
How have you been scoring on your practice CATs?
On any of those CATs, how many questions would you consider to be 'really hard?'
GMAT assassins aren't born, they're made,
Rich