About nitrogen alleviating fear and anxiety: laughing gas kind of does that, in fact does that roaringly, I know. But laughing gas clearly won't do, because it is an anesthetic, not poison! And nitrogen, would it actually make people go ha-ha before they die? Seems unlikely --- first, because nitrous oxide is different than nitrogen, and two, because someone inhaling nitrogen will die immediately, won't they, before having time to either laugh or cry? The making-them-smile-via-chemicals part will need to kick in well before the actual killing gas does, surely, maybe hours before.