I had a severe asthma attack and had to go to the ER. When I was being checked in, I was coughing severely,SOB, and sweating but my O2 level was 98%. After about an hour the tech came in to give me my second breathing treatment and he saw that my O2 level had dropped to 86%. He started me on oxygen right away. I was a bit surprised because my symptoms had abated and I was feeling better. After a couple of hours of oxygen and my final breathing treatments, I was taken off oxygen and observed for about an hour. In that time my O2 fluctuated between 88-92%. This satisfied their requirement of 90% so I was able to go home. I was just wondering why it dropped so quickly, particularly when I was feeling better? And are there any symptoms because I didn't feel any?