I had them once
Was on my way to work in the early morning and felt a cramp that wouldn't stop so I turned around and went back home. Barely made it in the door before dropping to the floor and doubling up in pain.
My boss came over and gave me a ride to the emergency room and I kneeled on the floor with my head in a chair groaning in pain while I waited my turn.
Doctors did their stuff and determined it was a kidney stone and then gave me some medication. I went from doubled up in pain to a smile in about three minutes
Short time later I was out the door with a $3,000 bill with no insurance.
Don't know exactly why I got one but I never properly hydrated while working construction and I had tried getting off pepsi by drinking apple juice which seems to help create stones.
Definitely very intense pain but I once had a toothache that had me rolling on the floor and feeling like my head was going to implode on fire.