Being an oldie, I have occasional colonoscopies in which I've always been anesthetized. My most recent one was a couple of years back. I'm not sure what happened, but during the procedure (after evidently going under), I was fully conscious of everything that was going on. I couldn't move and had no feeling for what was happening, but I could hear the doctors talk and could tell what was happening. It was much like a dream, but the most vivid dream one could imagine.
And I'm not an expert in this area, but my understanding is that during a colonoscopy they use a level of anesthesia called "conscious sedation", and the drugs they use also tend to have strong amnesia-inducing properties.
Anesthesia for surgery is more complicated and involves a cocktail of different drugs, administered in a particular sequence, tending to include paralytic drugs as well as special inhaled drugs that we don't even really know how they work (eg sevoflurane). It amounts to a much deeper state of anesthesia than the conscious sedation used in things like GI endoscopy and wisdom tooth extraction.
IANAA (I Am Not An Anesthesiologist) but I like to read about stuff like this and ask my doctors about it whenever it comes up for me.
I had a somewhat similar experience when I got my wisdom teeth out recently.
I consciously remember saying "Wow, this is working way faster than I thought it would" right before the dental assistant told me to go to sleep if I felt like it.
I have some memories of the surgery happening, like my head being jerked around when they pulled teeth out, but it was painless. Immediately after the surgery after I "woke up" I felt like I could remember quite a bit of the procedure but that feeling faded after some time and it all felt like a dream.
