what causes my o2 levels to drop , when I take my o2 off , my o2 levels read 72 , 80, 70, with o2 on , they read 92, 94, 98. I had a pulmonary function test , today, the respatorary therapists findings , was it wasn,t my asthma ,that what causing my o2 to drop without o2. What could be the problem?