Nitrogen Narcosis is the condition caused by the buildup of Nitrogen in tissue belonging to teh central nervous system(Dipak, <http://www.utdol.com/utd/content/topic.do?topicKey=ad_emerg/3059&view=print>). The effects start as soon as you get in the water but usually only become noticeable after 100 feet. Effects include the reduction of reaction time, thinking ability, and ability to do tasks requiring precision. It is best described as being similar to being drunk. Additional effects include hallucinations and loss of consciousness at extreme depths(Dipak, <http://www.utdol.com/utd/content/topic.do?topicKey=ad_emerg/3059&view=print>). It can be prevented by using an alternate air mixture. The two most prominent ones are Nitrox and Trimix. Nitrox is a mixture with less nitrogen, and more oxygen. It isn't very helpful with Nitrogen Narcosis because the additional oxygen content prevents divers from going below around 110 feet without risking oxygen toxicity. Trimix is used exclusively by commercial divers and technical divers. It has a high content of helium which has a significantly smaller narcotic effect than nitrogen. Nitrogen Narcosis can be cured almost immediately by ascending to a depth you were at before the symptoms started. Nitrogen Narcosis has no known long term effects, other than anything stupid you do while under the influence of Nitrogen Narcosis. (i.e. giving your regulator (what you breath off of) to a fish)