 Narcosis has been compared with altitude sickness insofar as its variability ( 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 narcosis . 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 narcosis 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 . 
