We live in such a world.
Narcosis while diving (also known as nitrogen narcosis, inert gas
narcosis, raptures of the deep, Martini effect) is a reversible
alteration in consciousness that occurs while diving at depth. It is
caused by the anesthetic effect of certain gases at high pressure. The
Greek word ναρκωσις (narcosis) is derived from narke, "temporary
decline or loss of senses and movement, numbness", a term used by
Homer and Hippocrates. Narcosis produces a state similar to
drunkenness (alcohol intoxication), or nitrous oxide inhalation. It
can occur during shallow dives, but does not usually become noticeable
at depths less than 30 meters (100 ft).
The relation of depth to narcosis is sometimes informally known as
"Martini's law", the idea that narcosis results in the feeling of one
martini for every 10 m (33 ft) below 20 m (66 ft) depth.
The intoxicating effect has to do with the partial pressure of the gas responsible, which here is good old nitrogen. Nitrous oxide is famous for producing a similar effect though at sea level you need to breath a gas which is mostly N2O. Even xenon can do it.
The conversion is 1 atmosphere of pressure to 33 feet of water. So 66 feet down you have 2 atm + 1 atm of gas = 3 atm.
You can have nitrogen narcosis at sea level if you have your world have a higher column of gas than ours and so a higher atmospheric pressure at sea level. Or have heavier gases (N2O would qualify) and get a higher atmospheric pressure that way, like Venus does (with a CO2 rich atmosphere). The nice thing is that "rapture of the deep" has been well described and is truly trippy, and you can lift that for your world.
from Jacques Cousteau's The Silent World
"'The light does not change color as it usually does underneath a
turbid surface. I cannot see clearly. Either the sun is going down
quickly or my eyes are weak. I reached the hundred foot knot. My body
doesn't feel weak by I keep panting. The damn rope doesn't hang
straight. It slants off into yellow soup. It slants more and more. I'm
anxious about that line, but I really feel wonderful. I have a queer
feeling of the beatitude. I am drunk and carefree. My ears buzz and my
mouth tastes bitter. The current staggers me as though I had to many
drinks. "I forgotten Jacques and the people in the boats. My eyes are
tired. I lower on down, trying to think about the bottom, but I can't.
I'm going to sleep, but I can't fall asleep in such dizziness. There's
a little light around me. I reach for the next knot and miss it. I
reach again and tie my belt on it. Coming up is merry as a bubble.
Liberated from weights I pull of the rope and bound. The drunken
sensation vanishes. I'm sober and infuriated to have missed my goal. I
pass Jacques and hurry on up. I am told I was down seven minutes.'