<unk>  while diving (also known as<unk> , inert gas<unk> , 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 (narkōsis), "the act of making numb", is derived from (narkē), "numbness, torpor", a term used by Homer and Hippocrates.<unk>  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 . 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<unk> , but it is impossible to develop a tolerance.<unk>  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.<unk>  may be completely reversed in a few minutes by ascending to a shallower depth, with no long-term effects. Thus<unk>  while diving in open water rarely develops into a serious problem as long as the divers are aware of its symptoms, and are able to ascend to manage it. Diving much beyond is generally considered outside the scope of recreational diving. In order to dive at greater depths, as<unk>  and oxygen toxicity become critical risk factors, specialist training is required in the use of various helium-containing gas mixtures such as trimix or heliox. These mixtures prevent<unk>  by replacing some or all of the inert fraction of the breathing gas with non-narcotic helium.
Nitrogen narcosis
Malignant hyperthermia
Anoxia
Barbiturate overdose
Histotoxic hypoxia
Pseudohypoxia
Hypoxia 
Hypothermia