Every year around the same time my oxygen level drop to 85 and i have to go on oxygen. But the rest of the year my level is 89 -92 and i dont need oxygen. It seem like i break down and have to build my self back up down. Sitting down right now my o2 is 93 but after 5minutes of walking i am at 88. But on at aday when i am not going through this 89 is good for me without oxgen. Can someone tell me why do i go through this down period.