Some components of breathing gases and their relative narcotic potencies: Gas Relative narcotic potency He 0.045 Ne 0.3 H2 0.6 N2 1.0 O2 1.7 Ar 2.3 Kr 7.1 CO2 20.0 Xe 25.6 The cause of<unk>  is related to the increased solubility of gases in body tissues, as a result of the elevated pressures at depth (Henry's law). Modern theories have suggested that inert gases dissolving in the lipid bilayer of cell membranes cause<unk> . More recently, researchers have been looking at neurotransmitter receptor protein mechanisms as a possible cause of<unk> . The breathing gas mix entering the diver's lungs will have the same pressure as the surrounding water, known as the ambient pressure. After any change of depth, the pressure of gases in the blood passing through the brain catches up with ambient pressure within a minute or two, which results in a delayed narcotic effect after descending to a new depth. Rapid compression potentiates<unk>  owing to carbon dioxide retention. A divers' cognition may be affected on dives as shallow as , but the changes are not usually noticeable. There is no reliable method to predict the depth at which<unk>  becomes noticeable, or the severity of the effect on an individual diver, as it may vary from dive to dive even on the same day. Significant impairment due to<unk>  is an increasing risk below depths of about , corresponding to an ambient pressure of about . Most sport scuba training organizations recommend depths of no more than because of the risk of<unk> . When breathing air at depths of – an ambient pressure of about –<unk>  in most divers leads to hallucinations, loss of memory, and unconsciousness. A number of divers have died in attempts to set air depth records below . Because of these incidents, Guinness World Records no longer reports on this figure.<unk>  has been compared with altitude sickness regarding its variability of onset (though not its symptoms); its effects depend on many factors, with variations between individuals. Thermal cold, stress, heavy work, fatigue, and carbon dioxide retention all increase the risk and severity of<unk> . Carbon dioxide has a high narcotic potential and also causes increased blood flow to the brain, increasing the effects of other gases. Increased risk of<unk>  results from increasing the amount of carbon dioxide retained through heavy exercise, shallow or skip breathing, or because of poor gas exchange in the lungs.<unk>  is known to be additive to even minimal alcohol intoxication. Other sedative and analgesic drugs, such as opiate narcotics and benzodiazepines, add to<unk> .
Nitrogen narcosis
Malignant hyperthermia
Anoxia
Barbiturate overdose
Histotoxic hypoxia
Pseudohypoxia
Hypoxia 
Hypothermia