narcosis
narcosis generally increases with depth, but it seems to be much more complicated than that. in my experience, it appears that your mental state can have a very significant bearing on the intensity of narcosis.
i've done some moderately deep dives with virtually no narcosis, but have felt strong narcosis on other dives to relatively shallow depths- of only 40m. (not very deep when talking about narcosis).
i can think of two such occassions....
the first happened when i accidentally scraped past a cliff face during a variable descent. this came as quite a shock, and unsettled me for a few moments, but i continued with the dive
the second time occurred when i had to spend an unexpectedly long time at the bottom of a variable dive before ascending.
in both cases, the increased mental tension seemed to trigger fairly intense narcosis. on both occassions the feeling went as soon as i left the bottom, and had gone by the time i reached 35m or so.
interestingly, many of my deepest dives (during which i felt hardly any narcosis) were done blind. i have wondered whether that helped because i didnt have a visual feedback to my brain which may have compounded the narcosis. i'm not certain whether this can happen...
alun