From the outset of your dive training, you are taught to follow a plan and monitor your depth, time, and gas pressure. These factors are key to your safety, and you learn early because there are plenty of wonderful sights to distract you.
At depth, narcosis compounds distraction; pretty fish are captivating, and your inattention to monitoring your gauges could lead to you going too deep, staying too long, or running low on gas.
Altered Perception / Hallucinations
Everyone has heard a tall tale about a diver talking to or trying to share air with fish. There are many variations, and they’re often extreme and told as funny stories, and while no one ever seems to know the diver involved directly, there is some basis in fact.
What I can vouch for is the diver who mistook a military helmet for a turtle and the diver that was convinced that a rope was hot to the touch.
These stories are entertaining post dive currency. But, what of the diver who goes deeper, oblivious to all danger, for a closer look at whatever enticing thing their nitrogen addled brain has conjured up?
Narcosis can make you forget how to do things like how to switch modes on your camera or, where the downline is, or more worryingly, what the display on your dive computer is telling you. It can also make you forget portions of your dive; after a deep dive, it’s interesting to see how your memory of the dive differs to that of your buddy.
Fixation / Perceptual Narrowing
Idea fixation can overwhelm to the detriment of all other factors. A diver could become obsessed with a malfunctioning torch. Turning it on and off repeatedly, shaking it, banging it; the problem is that they have not noticed their depth, where their buddy is, or even where they are.
Elation / Euphoria / False confidence / Impaired Judgement
You may find things extremely funny, a fit of the giggles is a clear sign of narcosis. Unlike other signs, laughter is obvious to your buddy, which is a good thing, unless they too are consumed with giggles at the same thing.
Many people enjoy the warm, fuzzy, happy feeling they have after a few drinks. This sensation is fine if you’re sat safely in your garden, enjoying the sun. Underwater false contentment could lead you to disregard limits.
Similarly, a couple of drinks might artificially boost your confidence, but narcosis underwater could lead you to push the boundaries beyond what is safe. Think about it, skewed judgment after a few drinks might lead you to believe you can dance; underwater, you might believe you’ll be fine inside a wreck. Your dancing might leave you shamefaced the next day but entering a wreck narced will be far worse.