I have a condition known as nocturnal hypoxemia. It was diagnosed in a sleep study. The doctor did a overnight pulse oxymetry test where they check oxygen saturation in your body. Its supposed to be like 98-99%. During my test, my O2 sat dropped below 88% for more than half an hour. That could lead to a stroke. I'm only 29. I don't know what causes it, I just know I have it. I have to sleep with an oxygen concentrator and breathe oxygen through a nasal cannula. Its a tube that goes in my nose. Its only at night though. I hate it. I hate having it on my face. The oxygen concentrator is a constant reminder of my disabilities.