Note that inhaling heavier-than-air gasses is _way_ more dangerous than inhaling - say - helium, because the latter naturally escapes, the former will tend to remain at the bottom of your lungs (if you stay upright) and will be difficult to exhale. It is a known problem with workers in certain kinds of welding processes that use argon as a protective atmosphere
That's an interesting point. I've never worried about helium much mainly because it is inert, but I suppose not having to hang upside down to flush it out is a plus.