Never had a kidney stone, but then I've never been in labor either, so I can't imagine those kinds of pain. I've battled ulcerative colitis for 30 years, though, and I can tell you that that's no fun (including the exams, colonoscopies, etc.) But leaving the below-the-waist stuff aside for the time being...

I've had 3 molars root-canaled (one tooth took 5 visits!) -- yes indeed, it's a horrible ordeal. So was the tooth infection that preceded the five-visit job. As leeneia says, anything that close to your brain and ears is a terrible place for an infection.

I've had three surgeries on my right eye, the first one being a reattachment of a detached retina. I was put under for the surgery, of course, but the recovery period was months long, quite painful (to muscles all over, as well as to the eye area), very tedious, and with the gas bubble just plain weird. No fun AT ALL. I tried watching mindless daytime television as RangerSteve describes, but with one eye converted to a ball of warm hamburger steeped in jalapeno sauce, the TV-watching was not taking my mind off the problem, just exacerbating it. Excruciating details are on this other thread: My retina surgery story

However, even having gone through all that, I would have to say that the worst surgical procedure I've endured is a lung biopsy with a bronchoscope. I do not recommend that one to annnNNNnnnybody. First of all, they don't put you under completely, because of the chance of suffocation from the procedure. What they do with the bronchoscope (a long tube with a light, a local-anesthetic-sprayer and a lung-tissue-snipper on the end) is to snake it up your nose, through your sinus passage to your throat, down your throat past your vocal chords, and into your lung. Once it's in there, the surgeon finds suspicious bits of tissue, sprays them with anesthetic to numb them a bit, clips them off your lung, and suctions them out of the tube. I remember every moment of this, including the numbed-but-still-palpable sensation of having the lung tissue pulled away and feeling it go up my throat and out my nose through the tube.

The worst part was gagging on the bronchoscope as it reached my vocal chords. They warned me beforehand about how it would feel in spite of the general and local anesthetics, but I couldn't stop the gag reflex or keep from struggling and rasping, "Get it out of me! Get it out of me!" They got me calmed down and got the tube down, after which I was of course unable to speak. Just had to lie there and endure. For days afterward, I was coughing up pink stuff. (At least I didn't have cancer, which is what they'd suspected!) I've never smoked cigarettes, but this is what you smokers out there have to look forward to...