Alright...I was SO nervous about getting this done - because of all of the reviews out there that say how much it hurts.
I had NO pain during my procedure - and little to NO sensitivity after. This was just done yesterday, and I am just fine. I really wish people didn't exaggerate the sensitivity to make others nervous.
The nurse who performed my whitening was in the room the entire time, and checked on me frequently.
If you are considering doing ZOOM - ask about the sensitivity and what the procedure will be like. I think the best advise I have heard it to BE SURE you are going to a good dentist who will protect your mouth, and explain everything.
In the end, my teeth are a bit whiter - and they even give you gel to do a touch up later, if you want them whiter.