Narcosis, in a nutshell, is caused by a buildup of gasses in our body. It shows up at deeper depths because we're breathing a higher concentration of gas at depth ... which tend to make the effects more noticeable. Note that I said "gas" rather than "nitrogen", because there is some evidence that oxygen building up in our tissues affects us similarly to nitrogen.
Nobody really knows for certain what causes it. Some scientists believe it's because the higher concentrations of gas in our body block impulses traveling through certain types of nerves in our brain. What we do know for certain is the symptoms, which are similar in many ways to other forms of intoxicant. These can differ from individual to individual ... and they can even affect the same person differently from one dive to the next.
The earliest symptoms affect brain functions such as concentration, memory and judgment. How those effects manifest themselves in the diver will depend on the individual. For example, a diver who is very confident in his or her ability might start feeling a sense of euphoria. But a diver who is not secure with their skills or surroundings may experience a sense of anxiety. In both cases, these symptoms may indirectly cause trouble
the former may lead to poor decision-making, while the latter may lead to stress.
As we continue deeper, narcosis starts to affect motor functions. Movement becomes more difficult and coordination is reduced. A diver may experience difficulty reading or interpreting the display on a dive computer or making adjustments for buoyancy control. Furthermore, the diver may develop tunnel vision or have trouble remembering things such as the agreed-upon maximum depth, no-decompression limits, or turnaround pressure. The diver may react slowly to directions or visual cues from a buddy, or make serious errors in judgment that can lead to an accident.
Deep divers may experience even more severe symptoms, such as hallucinations or even unconsciousness. This is the primary reason why people who do very deep dives tend to prefer to use a breathing gas with helium in it, which is a very light and inert gas that doesn't exhibit the same symptoms.
Some divers are more susceptible to narcosis than others. Some divers will not recognize the symptoms in themselves, or will recognize them in their dive buddys behavior before the dive buddy realizes that they are narced. Our physical and mental state can have a significant impact not only on our susceptibility to narcosis, but also on how the symptoms manifest themselves. Symptoms can vary within the same diver from dive to dive. Certain factors, however, appear to increase the effects of narcosis. These factors include:
Inexperience, or a lack of confidence in ones abilities
Fatigue or exertion
Cold water
Rapid descent
Poor visibility
Carbon dioxide buildup (hypercapnia)
Task loading
The good news is that narcosis can be managed by the diver. Ascending to a shallower depth will reduce the symptoms progressively as you ascend
or will make them go away altogether. However, since narcosis is predominantly a mental disorder, even such things as focusing on your gauges or concentrating on a task will help make the symptoms more manageable. But keep in mind that if you are narced, the chances are very good that your dive buddy will be too. So a prudent thing to do would be to signal to your buddy to ascend a little bit to reduce the effects. All it usually takes is 10 or 15 feet in most cases to reduce them to the point where they are more manageable.
... Bob (Grateful Diver)
