The only reason I doubt that theory is because the pain would cause the heart to race which would be noticeable on the monitors and other autonomic effects like sweating and vomiting.

i've had three procedures where my anesthesia was insufficient. two, fortunately, were dental and i could grit my mental teeth for five minutes. one was a gastro surgery and i think they just forgot to give me the ForgetMeNow because i was wide awake and talking to them the entire damn time while they rummaged around in me.