[wl]

Anesthesia gasses aren't paralytics. MAC is not about chemically preventing muscles from activating but depressing consciousness to the point that muscles don't move in reaction to painful stimulus. Chemically blocking muscle movement (neuromuscular blockade) takes an actual paralytic like succinylcholine. Pain control is yet another, separate factor. Even with depressed consciousness from a gas/propofol infusion and neuromuscular blockade, blood pressure (which is part of standard monitoring!) still will spike in response to painful stimuli. So usually, anesthesiologists will give an opioid in addition to gas/propofol to control pain, even if the patient isn't conscious and wouldn't be consciously aware of the pain of surgery.

The nightmare scenario you describe is when a patient has neuromuscular blockade, is not being given sufficient gas/propofol to depress consciousness, and has inadequate pain control that isn't being picked up in the blood pressure either because the anesthesia provider isn't paying attention or is controlling blood pressure through drugs to the point they can't see anything. If, for some reason, that kind of anesthetic is medically necessary, benzodiazepines can (if tolerated) prevent memories from forming lessening the chances of psychological trauma.