The most dangerous person in the water is the one who does not realize that they are narc'ed. That doesn't mean that you can't learn to handle the narcosis, but I won't dive with someone who claims immunity to the process. Here's the deal...
How do you know that you are impaired on the surface? First there is that "swagger" from losing your balance. It's pretty hard to sway under the water since you are buoyed up by it so you can't rely on that! Second, you have slurred speech. Not too many people try to talk under water so that's out as well. The two main symptoms of impairment are now completely masked. No wonder he didn't "feel" a thing. That's the problem with narcosis; it sneaks up on you!
Narcosis also affects people in different ways. Some it makes paranoid (such as you were feeling), some it empowers (very scary!) and others just sort of mellow out to the max. If you were too paranoid to get the reel, your buddy might have been able to retrieve it easily.
There are several ways to cope with narcosis. Avoidance of deep diving is what is taught in the OW books and that's not always the best way to deal with it. If you aren't sure, take a deep diving specialty with someone who understands the very real dangers of getting narc'ed. Avoid the cowboys who claim that they never get narc'ed... that's just crazy talk!
The best way to know that you're impaired is to check your depth gauge. Every atmosphere adds to your bovine index. The deeper you go, the more you act like a cow. I can be pretty sure that if you are at 4 atmospheres that you are not as agile a thinker as you are on the surface. Plan accordingly. BTW, while I don't "feel" narc'ed at 80 fsw, my right shoulder stops hurting!

I like the effects up to a point, but this is when I start making allowances!