I also had a colonoscopy not very long ago to remove a pre-cancerous polyp in my colon. They just gave me Entonox and I was absolutely fine on that. In fact I felt so relaxed, and on top of the world afterwards, perhaps because the procedure was so quick, easy, and painless. And I could watch it all on a big screen. I was greatly encouraged by how pink and healthy my colon looked, apart from the polyp! I guess everyone's is like that, until or unless something goes wrong.
I can only presume that your procedure must have been a lot more complicated and painful for you to have needed midazolam and fent. Maybe they just use Entonox for easy cases in the UK, and anything more invasive I guess they'd need to step things up. I'm not sure what country you're in, or if your procedure would have been more invasive.
It obvious we're all getting older on here, with many of us now starting to talk about medical conditions, procedures, and surgeries. It's all down hill from here

Although I obviously hope that all of us have as many healthy years remaining as possible. I was lucky to have got this polyp picked whilst being scanned for a different condition. If it hadn't been detected and removed, it would have turned cancerous and infected my colon within 7 years. And by that stage, it might well have been too late to do anything about it, other than the horrors of chemo-therapy etc. All of that has now been avoided from that particular polyp. I'm now trying to eat better, so that hopefully I don't get another one.
Unfortunately you cant just contact the hospitals every year and say that you want to get radiotherapy scanned or CT scanned for cancerous growths. It could save many lives, but would be way too expensive. Plus I gather that the radioactive scans especially can also pose a slight risk of causing cancer, but usually the risk benefit is in favour of the scans, when presenting with known conditions or issues.