Narcosis is always anaesthesic, but not necessarily inebriating.
Anaesthesic State: Total or partial loss of sensation, especially tactile sensibility.
Inebriated State: Exhilarated or stupefied.
Narcosis (anaesthesic) is likely to be present on any deep air/nitrox dive. The very fact that the primary and initial effect of narcosis is anaesthesic, means that the diver is less aware of any physiological changes that may effect their capabilities.
When a diver has sufficient experience that their core diving skills are instinctive, then they are unlikely to notice that narcosis. This is because narcosis primarily effects problem solving and stress reactions. If at an instinctive level, diving skills such as buoyancy, trim, navigation, buddy skills or even awareness of depth/time/gas can be easily performed even when the diver is otherwise significantly narc'd.
If you're enjoying a tranquil dive at depth, but not forced to problem solve, react to the unexpected or deal with stress, then it is possible that you wouldn't 'notice' even a relatively high degree of narcosis. It is a hidden danger.
That is what some divers mistake for 'acclimatization' to narcosis.
Divers only tend to notice if the narcosis becomes inebriating, or when they are called upon to problem solve or do other non-instinctive tasks. This can lead to a false sense of confidence in their capacity that is only exposed when an emergency or stressful event occurs (and inebriation becomes an apparent symptom).
As others have already mentioned.... CO2 retention may also cause a rise in the actual level of narcosis. Which causes a 'double-whammy' impact.... because CO2 levels tend to rise in emergency or stressful scenarios.
