Its true, you really dont know what to expect, you cant possibly memorize every lab value and medication that exists, no one can...Its a challenging test but its absolutely possible to pass. I STRONGLY recommend the Kaplan review, its a bit expensive but totally worth it and those questions are the closest to the NCLEX. They give you online resources with tons of questions and their rationales. I recommend doing that as practice, it also tells you areas that your weak in also so you can brush up on those areas. Dont make yourself crazy though....I was always weak in labor and delivery and never got those questions on the NCLEX. Practice for a few weeks and you will be confident.
One more thing, you may be asked the same question on the NCLEX multiple times, but worded differently....DO NOT CHANGE YOUR ANSWER. They will try to shake your confidence and you will think maybe your doing something wrong but your not. You know your stuff.