To have an upper endoscopy is to be violated, both orally and gastrically. Despite a stinging, numbing banana-flavoured spray on the back of the throat, the front end of the countless metres of black cable they feed into you is incredibly uncomfortable. You have to swallow it as it enters your esophagus, as it's about a centimetre in diameter. That wasn't too difficult this time (my second), but it was still fucking horrible. Last time I retched the entire time it was inside my body - this time, I managed to curb that, a bit. Retching unstoppably for 5 minutes is REALLY nasty.
A ring of plastic between your teeth stops you from biting through the endoscope, and despite an assistant sucking the fluids away from your mouth, you feel at most times like you're very much in danger of choking on your own saliva.
The thing I forgot, from last time, is that you burp. Around the tube. They feed air down the cable, presumably to keep the camera(s) clean, and you expel it periodically. Your eyes water constantly, as the various portals in your digestive system attempt to close, but are blocked by the 10mm cable. I don't think my nose streamed too much this time, but I'm probably wrong, as I do remember a lot of mucus. It's hard to choose to remember specific details, as you're effectively in shock at the time.
Certain specific details are very vivid, however. It's bizarre, watching the different coloured fluids flow through the extraction tube - colourless, yellow, brown, red. Red from the biopsies, which they take with a tiny (about 0.8mm) metal claw on the end of a wire. It's like a really small egg grabber, and they use it to simply gouge and tear chunks of you to be examined later.
The cable is fed in with a surprising amount of force, presumably to shorten the experience. It is also withdrawn very quickly, which is a vast relief. The end of it is prehensile, allowing them to direct it through the stomach and intestines without it catching, scratching or getting stuck, and the sensation is unique and unpleasant, to feel something poking and writing inside you. At the same time, your throat still believes that it's no more than a few centimetres down, and if you stop thinking your tongue tries to extract it, like a piece unchewed spaghetti.
Being deep-throated loses all of it's appeal.