As it has been said before, I just have to say it again. If you dive, you experience the effects of Nitrogen Narcosis. You may not know it, but you do.
So, having said that, I have had a few instances where I knew I was narc'd, but most where I did not feel the effects. I have had hallucinations and that was a very interesting experience that scared the bejeezus out of my instructor. Both he and I should have known better than to have me in that position so early in my diving career. But, we were younger and inexperienced. I think we both know better now. It is a good thing it turned out ok.
I have had the really paranoid feeling and also where I felt I was having a hard time breathing. An ascent helped both situations and after I felt better, I descended again and continued the dive. However, if you don't feel comfortable continuing a dive after ascending, then call the dive then and there. I think the one where I felt like I had a hard time breathing could have been a combination of Nitrogen Narcosis and CO2 build up. I also felt like my wet suit was too tight. On that dive my buddy unzipped my jacket and I felt better. Who knows what made me feel bad, could have been one or all 3 of those things.
In any case, pay attention to how you feel and never, never hesitate to call a dive. That way, maybe you will be diving for over 20 years, too.