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.