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 νάρκωσις (narkōsis), "the act of making numb", is derived from νάρκη (narkē), "numbness, torpor", 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). Except for helium and probably neon, all gases that can be breathed have a narcotic effect, although widely varying in degree. The effect is consistently greater for gases with a higher lipid solubility, and although the mechanism of this phenomenon is still not fully clear, there is good evidence that the two properties are mechanistically related. As depth increases, the mental impairment may become hazardous. Divers can learn to cope with some of the effects of narcosis, but it is impossible to develop a tolerance. Narcosis can affect all divers, although susceptibility varies widely among individuals and from dive to dive. The main class of diving that deals with its prevention and treatment is scuba diving at substantial depth. Narcosis may be completely reversed in a few minutes by ascending to a shallower depth, with no long-term effects.
For an inert gas the narcotic potency was found to be proportional to its lipid solubility. As hydrogen has only 0.55 the solubility of nitrogen, deep diving experiments using hydrox were conducted by Arne Zetterström between 1943 and 1945. Jacques-Yves Cousteau in 1953 famously described it as "livresse des grandes profondeurs" or the "rapture of the deep".Further research into the possible mechanisms of narcosis by anesthetic action led to the "minimum alveolar concentration" concept in 1965. This measures the relative concentration of different gases required to prevent motor response in 50% of subjects in response to stimulus, and shows similar results for anesthetic potency as the measurements of lipid solubility. The (NOAA) Diving Manual was revised to recommend treating oxygen as if it were as narcotic as nitrogen, following research by Christian J. Lambertsen et al. in 1977 and 1978. See also
Hydrogen narcosis – Psychotropic state induced by breathing hydrogen at high partial pressures
Oxygen toxicity – Toxic effects of breathing oxygen at high concentrations

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Bennett, Peter; Rostain, Jean Claude (2003). "Inert Gas Narcosis". In Brubakk, Alf O; Neuman, Tom S (eds.). Bennett and Elliotts physiology and medicine of diving (5th ed.). United States: Saunders. ISBN 0-7020-2571-2. OCLC 51607923. Lippmann, John; Mitchell, Simon J. (2005). "Nitrogen narcosis". Deeper into Diving (2nd ed.). Victoria, Australia: J. L. Publications. pp. 103–8. ISBN 0-9752290-1-X. OCLC 66524750. U.S. Navy Supervisor of Diving (2008). U.S. Navy Diving Manual (PDF). SS521-AG-PRO-010, revision 6. U.S. Naval Sea Systems Command. Archived from the original (PDF) on 2014-12-10. Retrieved 2014-01-21.