Nitrogen narcosis - diving while being drunk?

Nitrogen narcosis - the name explains it. It's a state of mind which is caused by breathing nitrogen at high partial pressure. The effects become noticeable at a depth of about 30 metres and become more hazardous when diving deeper. Diving beyond 40 metres while breathing air (which consists of 78% of nitrogen) is strongly dicouraged by most proffesional organizations. Narcosis may be comlpetely reversed by ascending to a shallower depth with no long-term effect.

Nitrogen narcosis has an an anesthetic effect on diver, similar to being drunk.  It may cause a diver to feel either euphoric or stressful emotions which can affect rational judgment and therefore be very dangerous. It also slows the diver's reaction time, thinking and an ability to reason. There are even recorded cases of underwater hallucinations!

While it's impossible to develop tolerance to nitrogen narcosis, proffesional divers learn to partially cope with the negative effects. When diving beyond 40 metres various mixtures of breathing gases are used - such as trimix and heliox - which replace nitrogen with non-toxic helium.

source: https://www.thoughtco.com/what-is-nitrogen-narcosis-2963052