I sometimes have problems getting 100% oxygen from breathing. It is because my nose has reduced inhailing capability, it was broken as i was a kid... I see now, that if i go outside this problem virtually doesn't exist, but in my flat i get tired easely, and fell asleep sometimes. Normal ways like ventilation don't work that well and in the winter are rather impossible. Are there ways, special air conditioners or something medical, which can increase the oxygen level or regularely "pump" the fresh air from outside?? it is not about "my particular flat", it is in any flat . I.e. if many people are in the room without open windows i might fall asleep or experience blackout:(