I did that at night . It was before I was diagnosed with COPD and put on oxygen . Be sure you are breathing regularly . I sometimes found myself holding my breath when I was doing a task that took concentration . It is an in voluntary response . I was puzzled too. I never spoke to anyone about it . I now think it was my body needing oxygen. Keep asking your doctor or get to a pulmonologist. I should have had oxygen long before I got it . It actually let my disease progress without any help . Blessed Be, Crystalena