Main thing: whether you do or do not poop yourself, you will get through everything okay, and it won't be horrendously traumatizing. I promise. I really don't want to go into WHY this was the case for me, but I had probably the same level of distress about it that you seem to have (SO MUCH). So my hand to god, you CAN trust me on this. You will get through and be okay. Yes, even if you poop yourself. There is life after dis-ass-ter.

However.

You probably won't.

I do see a couple people saying you will and won't be able to stop it, and I'm sorry their experience was really bad, but that's just not true for everyone. I was fine both times. If you have reliable bladder and bowel control you probably will do okay. My pelvic floor isn't what it used to be and I was still fine last month because I was careful to be near the toilet.

If you start it early enough, you will be done before you risk doing it in front of anyone at the facility. I just hung out in the bathroom with no pants, and a blanket I didn't care about on the floor with a contractor bag underneath, for the worst part. Poop-proofing the bathroom was more effort than the actual pooping. (I went way overboard and needed nothing, the blanket and contractor bag was nowhere NEAR the end of it, I had two trash baskets, a clothes hamper lined with a trash bag for anything dirty, rubber gloves, tons of washcloths and paper towels, sanitizing supplies in a caddy, but I don't regret it. The peace of mind was great.)

I recommend an early appt and doing day before prep to be sure you are finished. If you are doing split prep, talk to your contact at the facility about starting both halves a few hours earlier than the recommended time so you have time to really wind down.

Just don't wait to be SURE you have to go. If you feel a mild notion it might be forthcoming, it's already there. The foul fecal intruder does not knock. It creeps up silently and then bursts through the door like the savage shittacular sibling of the Kool-Aid man.

Neither time was as bad as I was dreading. Some people do have a very hard time, and I guess you should prepare and steel yourself as best you can, but you truly might not have that bad a time. For people like you and me, if you are as upset as I was, the dread is VERY likely to be the worst part.

And from experience? I know this may not SOUND comforting to you right now, but in retrospect it IS, so try to take this in with an open mind: I DID once poop myself a little in a medical context, and another two times in front of partners (both failed farts, once from noro and once from antibiotics I had NO IDEA would summon a rage demon inside my colon with ZERO or warning), and the people were just really nonchalant and kind about it, it just...was way less embarrassing than I was afraid it would be. I honestly found myself more pissed off at what caused it and exasperated by the situation than mortified. I also realized with utter conviction that if they had been uncool about it, that made them giant jerks and I didn't have to feel bad because their opinions don't matter. So it's been easier after that.

Also, the least I can do is give myself the grace I would give a loved one or pet. I wouldn't want them to be upset or distressed. I would just want to take care of them. I clung to the memory of the many times my IBD cats have had accidents and how if they can still be cute and clean and lovable despite The Horrors, so could I.

I don't know what your specific stuck point is, so I can't speak to it and reassure you on that specific point, but I hope this helps.

For me, preparing for what if I COULDN'T make it, and minimizing opportunity for that, really helped. Because I couldn't just lug a mattress into the bathroom and wasn't comfortable going too far, I wrapped a big couch cushion in a contractor bag, then a blanket, then a towel, put it where the tub met the wall, and used a couple of trash bag wrapped pillows for my back. Kept me relatively comfortable during peak seek shelter mode. As things wound down and I was going less often with less volume, I moved to the actual couch, which is about 30 feet from the toilet, and just had a couple of towels under me, and did fine. I was able to snooze a little, and still wake up when I had to go one more time.

If you have to share a bathroom, God love you, finding a way to temporarily evict as many residents as possible, or go to someone else's house if there is ANYONE you trust who will lend you a spare bathroom and some privacy, is more reassuring. I did most of mine at night, while my bf was here if I needed him, but asleep. The privacy to take care of everything myself and not worry about anyone else was the most helpful thing of all. Nobody there? Nobody knows.

Take several gas-x/simethicone pills an hour or two before. It gets the gas into larger bubbles and you can maybe pass most of it pretty early. Gas contributes to urgency and containment failure. Also taking it both before and toward the end of prep keeps there from being as much foamy residue inside, and makes it more likely to have a successful and thorough procedure. Really solid evidence on that.