When I had my kidney stone attack, I was quite literally in agony. I never thought the human body was capable of feeling that kind of pain and I literally thought I was dying! They shot me up with dilaudid at the ER and then sent me home with dilaudid pills for later. I think I only took 1 or 2 because they're heavy, heavy duty morphine derivatives that knocked me out pretty hard but I needed it because I was in so much pain!
Passing the stone wasn't the painful part. My urologist later told me the pain wasn't due to the movement of the stone, it is due to the stone blocking the urine from being able to move through the system and the backup is what causes the pain. I had no idea until he told me but I guess it makes sense.