Don't know if this counts as an upper GI "procedure" but I'll describe the MRI as well since I had no idea what that would be like.
I think the machine they used was a 1.5T Samsung one. The nurse asked me to change - completely, except underwear - into a gown, after leaving any metallic objects behind. I then headed into the room, which was bloody cold - I'm guessing to help cool the superconducting magnet. They asked me to lie on the bed, which is relatively comfortable if a bit hard, then put a coil on me (it was an abdominal MRI) which looked like a grid of 10cm x 10cm squares of thick plastic that covers the whole chest, and then a thick blanket for which I was grateful at this point as my hands were turning blue.
The first scan is done without contrast, so no injection yet. I asked for earplugs which was necessary I think as the noise is pretty loud. They put them on for me and then put headphones on. You get a little air "pear" that you can squeeze if you have issues to speak to the nurse, that's placed in your right hand. Then they belt you up, I suspect to keep the coil in place, it's a velcro strap around the chest but not super tight (you can probably get out of it if necessary).
Then began the interminable series of test. Officially, it takes 15 minutes but you never know when it's going to be over since you can't see a clock. The tube is not so bad honestly, if you move your head a bit you can see the openings on either end. You're asked to hold your breath around 15 seconds for many scans. When you hold your breath, you can hear the noise of each scan, coinciding with a warming feeling in a small section of your abdomen - I immediately thought of reheating chicken in a microwave. It's not "hot", just a mild warm sensation like you get after drinking warmish hot chocolate. In movies, they have the sound be clonking noises but most of it is actually closer to alarms, either a long fire alarm or short bursts of a medium pitch alarm, a whining sound. That's why it's quite jarring, and why the headphones are a good idea.
Well, the 15 minutes really took their time even if staying still was easy. I think if you come in knowing it will feel really long you can prepare mentally for it, when they say "15 minutes" you think "oh, this will be over quickly" (ironically, the opposite was true for endoscopy, I thought it'd be interminable but thanks to sedation it was over in a flash).
They wheeled me back out of the thing, undid the strap, the nurse came over and inserted the IV. I was bloody cold again but she got it easily and it didn't feel like much. I thought that was the injection but then they brought two syringes the size of cyclist water bottles and hooked that up. I was told to be very still and follow instructions attentively as the contrast scans cannot be redone on the same day, which would mean another round some other day (at $1,700 a round! I hope you Brits enjoy your NHS). "Just 5 minutes".
Well, the 5 minutes took just as long to pass as the 15 minutes previously. But since you're lying down it's easy to close your eyes and just wait it out. Contrast scans feel the same as not contrast scans, except for the part where you're a bit anxious not to screw it up so as not to go through the whole thing again. I felt nothing even as the contrast was being injected and had no reaction. The only feeling was the poking of the IV initially, but I rapidly forgot about it - like a mosquito bite.
Then they asked me if I wanted to keep the IV, I said yes, cos I'm going upstairs for the endoscopy, so I got out of the fridge, changed back, went upstairs and go the endoscopy.
All in all an alright experience, but I'm not saying anything new here. I wish they had given me the pictures on a USB stick so I could enjoy looking at my organs in 3D and sharing them with my family, but alas it's all printed out on that negative paper they use for the ultrasound as well, which is quite hard to read and copy.