How will I likely react to Ativan as a premedication?

I'm getting my wisdom teeth removed in two weeks and I specifically told the surgeon I did not want "Laughing Gas" (Because I had a really bad reaction to it when I was younger) or to be put under general anesthesia (Because I just don't). Even though I asked for him to just use Novocaine, he prescribed me "nerve pills" -- 4 mg of Ativan. I do not take any medication that isn't OTC unless it's something like an antibiotic, so I don't know how I'm going to react to this. So my questions are: Exactly what kind of reaction(s) can I expect to have? Is 4 mg a high dosage? And approximately how long will it take for any effects to wear off?