If you really want to feel the effects of narcosis go for a joy ride in a chamber. I get hit pretty hard by it and have felt it as shallow as about 25-27 metres but in the chamber i started to feel the effects at 2 metres. Yep 2. I think the environment has a lot to do with its onset as well. Cold dark water seems to bring it on quicker than warm clear water. On a 2 week trip to the Solomon Islands we were doing 60-70 metre air dives everyday and i felt less and less every dive. We did a 40 metre dive late in the trip that felt like it was 10 metres. My head felt real clear with no real effect.

Matt