[nradov]

Nitrogen also causes cognitive impairment. It is essentially a very weak anesthetic. If you can replace all of the nitrogen in your breathing gas with helium then you'll probably gain the equivalent of a couple IQ points (although obviously that isn't generally practical).

[ndsipa_pomu]

Nitrogen narcosis is especially relevant to divers. Recreational SCUBA diving is usually limited to around 30m depth and some divers will start noticing effects (basically like getting drunk) near that depth when using air in the tanks. This is why different mixtures (e.g. trimix) are used at increased depths, though there are other important effects of breathing air at pressure such as oxygen toxicity.