The glucose screen you may have had before is called the Breakfast Tolerance Test. A very specific amount of food is eaten after a 12 hour fast (usually overnight) and exactly one hour later your blood is drawn. Does this sound familiar? This screening method has been pretty thoroughly reseached, the idea being that a woman can get the same grams of glucose from FOOD instead of that nasty glucola stuff, and get results that are equal to that same nasty stuff.
The drawback is that you have to fast overnight, whereas the glucola stuff you can do anytime.
A WORD OF CAUTION!! If you decide to do the screen and do the glucola, BE SURE to eat a very good meal (beans and rice for example) a couple of hours before the test. This mass of carbohydrates will stabilize your blood sugar enough to withstand the shock of the sugar and will give a more accurate reading of your bodies reaction to sugar.
Good luck! And you know, there's lots of controversies around even doing glucose testing if you haven't had problems in other pregnancies, no family history of diabestes, etc. A random fasting blood level can be a good indicator if your body's doing ok, or if you could really benefit from doing the full on screen.
hope this helps.
PS I personally did the Breakfast Tolerance Test and didn't feel nauseated, dizzy or anything! (it was eggs, toast, orange juice and milk)