You aren't (or shouldn't be) put under general anesthesia for a colonoscopy. They use "conscious sedation", in the USA typically achieved with intravenous propofol. You are technically conscious, but very sleepy and unable to form memories while sedated.
But yes, general anesthesia is really wild stuff. Even more wild when you learn that we don't know how they actually work, other than that they work.
They gave me a "sedative" for my colonoscopy. They just said it will make me really relaxed and maybe sleepy. I wasn't sleepy at all but boy was I relaxed! I remember laying on my left side, the doctor behind me controlling the scope, and the nurse in front of me but not obstructing the views of the monitors that were also in front of me. I was getting an awesome inside view of my guts! At one point I was feeling some pain and making some noises about it and the nurse told the doctor to hold on, apparently there was a pretty tight turn and she kneaded my guts so they could negotiate it. They did find a polyp and showed it to me on the monitor, TBH you have to have a trained eye to recognize those, so they biopsied it right then an there. The results came back a few days later saying it was benign. Unfortunately since they found a polyp they have me on a five year colonoscopy schedule instead of ten.
For those fretting about getting a colonoscopy, like I was, let me tell you it's no big deal. I've had dental cleanings that were more uncomfortable. In fact, there was nothing about my colonoscopy that was uncomfortable. Getting your guts cleaned out in preparation for the colonoscopy? Yeah that's a different story but the actual procedure itself is a big nothing burger.
I don't know how common the different methods are but in my case I was certainly out and that was the intent. They did use propofol and it was like the time I was out just didn't happen. I have memory issues that seem to be related to sleep issues but they were not affected by the sedation any way I could tell.
It could still be sedation only. Sedation for colonoscopy is usually done with propofol.
Patients don't always notice they're semi-awake, and most don't remember the procedure. It's perfectly normal. I you had an airway in place and were mechanically ventilated, then that's general anesthesia.
While my memory isn't 100% clear, I'm fairly sure I had a mask and I clearly remember the anesthesia person saying I would be out in a few seconds (which is what happened). There were three people doing the procedure, one just on the anesthesia (nurse anesthesist I think), and it was done in a hospital complex. When they woke me up I first thought they must want me to move to a different position before they start but it was done (I don't remember how long it took but it wasn't that quick even though they didn't find any issues). While convenient to not feel any pain (not even any discomfort that I can recall), it is unsettling to have a hole in my life like that. I can see how those drugs could be misused, although at least I can remember everything before I was out and after I woke up at least as well as I can remember anything (maybe better since I was worried about what they might find). The time I was out didn't feel at all like sleep. And the haze managed to fully clear not long before I went to bed that night so it didn't even help me get to sleep faster :/.
They use conscious sedation for both. It's unlikely you got general because there are significantly greater risks involved with administering and recovering from general anesthesia. For conscious sedation, all they have to do is give you an oxygen mask (or the tube that sits under your nose, aka "nasal cannula").
But yes, general anesthesia is really wild stuff. Even more wild when you learn that we don't know how they actually work, other than that they work.