The good new is that this may not be an "Either/Or Question"!
Gastric balloons are most commonly placed endoscopically. That means the surgeon or gastroenterologist will put a long tube (endoscope) down your throat that has a camera at the end (so they can see!). They can then pass the balloon down into your stomach and inflate it under direct vision. Before I do endoscopy, I generally give a spray numbing solution to the back of a patient's throat. This just seems to make the procedure a bit more tolerable for the patient. Most of the time, they will ALSO give you sedation prior to this procedure. The medicines are a combination that not only help you relax, but also give you temporary amnesia so that you usually don't even remember the balloon being placed! Most patients remember being in the holding area and then the next thing they remember is waking up in the recovery room. You'll be awake the whole time they place the balloon, you just don't remember it.
Getting a balloon placed really isn't that bad and for many patients it's a great way to get them to lose some weight before their definitive procedure. Good Luck!