@SusanEllen66 something that periodically affects me is a sinus infection that migrates down into my lungs. I have asthma and allergies and this creates phlegm in my lungs that interferes with oxygen absorption. I will feel tired and when it gets bad, I notice my heart rate goes up more than normal. The solution is something I learned as a pre surgery preventative when doctors had me use antibiotic ointment inside my nose to clear any staff infections. I was prescribed mupirocin and it works great for this. It will cause phlegm that needs to be cleared as the lungs are flushing out an infection. I feel ok when this happens except for being tired and exhausted from not enough air. I will be fine after about 5 days of treating this and my doctors have given me a prescription to use as needed,