It can be the difference between between feeling like you're suffocating, not getting enough oxygen to rest enough/sleep well.

I notice a difference if I move between a ventilated room vs congested one. I suppose it depends on what's causing the concentration. If it's human breath, I'll smell freshness. If it's e.g. burning a portable gas heater (common in my part of the world), I'll feel like I'm not inhaling smoke (probably small amounts of CO).

A few years ago, I would sometimes wake up at night and open a window wide, or go open the outside door and stand there for 5-10 minutes.