I had this done a while ago for the same reason as you...To rule out other problems before having my gb out.
The procedure is simple...And I was awake through the whole thing. Most people are asleep for it. They spray a numbing spray(this stuff tastes horrible--so be warned) in the back of your throat to numb your gag reflex and then you are given the anesthetic--usually you are asleep or unaware what is going on after this point. If your awake they will put a round plastic thing in between your lips to hold them apart and stick the scope in there. It just feels like butterflies in the stomach. The whole thing took me about 5 mins.
Nothing to worry about.