Glucose test question

So I will be getting this done in two weeks and I'm a bit confused/concerned. I have low blood sugar, have had it since middle school, and have been told not to eat a lot of sugar in on sitting my since.  So I'm kind of freaked out about taking the glucose test and my sugar dropping a lot a few hours later to very low.  Did that happen with anyone else? How did you feel during, after, etc...with the test? I'm probably just concerned for no reason, lol but thought I would ask :) thanks!