Hi vatreni,
These two practice scores are not as far apart as they might appear. GMAC has publicly stated that the Official Score that you earn on Test Day is within +-30 points of actual ability. Assuming a similar 'swing' in how practice CATs function, these two scores point to a general ability in the high 600s.
Have you had a chance to review each of these CATs? Can you define WHY you're getting questions wrong? How many questions did you get wrong because of a silly/little mistake? If you let too many of those questions slip away, then your score will be impacted.
A 2-3 week 'vacation' from studying could very well affect your test-taking skills, but there won't be any way to quantify that impact until you get back from the Holiday and start your studies back up.
GMAT assassins aren't born, they're made,
Rich