I have had nasal blockage for 10+ years. One nasal would be completely blocked up and the other open and vise versa. It's not allergies, cold/flu as I've tried any and all medications. Recently it has taken a toll where I would just feel like I ran a marathon. I would be out of breath, fatigued, and almost about to pass out! I think it might have to do with this nasal blockage but I'm not sure if lack of oxygen is linked to these symptoms.