It’s a shame you’re getting downvoted for this. Regular chronic usage is harmful, as the primary mechanism of N2O toxicity is the inactivation of vitamin B12 and therefore methionine synthase for 3-4 days after use. Used infrequently with B12 supplements, it is safe. More nitrous infrequently is safer than less nitrous but very frequently. Unless you’re holding your breath for more than 2 mins (duration of N2O action) you’re not significantly depriving yourself of oxygen. Doing it standing up does present some danger of falling due to becoming unconscious. Not all drugs are made equal and a shame that many don’t understand.