Years back Chuck and I recorded an episode on anesthesia, wherein we got to the bottom of the phenomenon of why redheaded people require more anesthesia than people born with hair of other colors. (To be short, it's in their genes.) At the time, Chuck and I didn't stumble across a horrific anesthesia-related item called anesthesia awareness. You can be sure that we will soon record an episode on it, but to summarize, it is the phenomenon of waking up in the midst of surgery and experiencing it all: the pain, the tearing, the handling of organs, everything except the sights, since the eyes are taped and bandaged shut during surgery. Since modern surgical techniques employ drugs that paralyze the patient, there's no way for the person being operated on to alert the surgical staff that they are awake and in unbearable pain. Typically, people have difficultly remembering the experience, but tend to form PTSD as a result.
The discovery of anesthesia awareness has illuminated a flaw in the practice of anesthesiology: That anesthesiologists don't really understand how their drugs work. To understand them, they would have to understand how human consciousness works and we don't even know how to properly define consciousness at this point, let alone understand how it is produced and by what. Only after we reach that point will the field of anesthesiology be able to fulfill its stated goals of completely removing consciousness from a human being and restoring it fully once more with no ill effects.
While you wait for us to get busy recording an episode on anesthesia awareness, be sure to take the time to read this exceptional Atlantic article that explores the phenomenon, as well as the questions of what makes us conscious.