Apparently, when you use N (usually under some sort of hood or mask that makes sure you don't accidentally breathe in normal air) you need to take care that the CO2 you exhale, is being sucked out of the hood. While N itself will likely not cause problems, it being a completely neutral gas that is just a filler substance, a placeholder for 'nothing,' the lack of oxygen might, and the presence of much CO2 would certainly cause you reflective panic and discomfort... it seems that therefore, you need to make sure that this CO2 gets transported out of your hood for 40 minutes or so. There's a detailed posts about it somewhere in the N-thread... please look for it (and tell me if I misunderstoof this, because I find it ridiculous and appalling).
