Recently, I have been feeling a little shortness of breath. I found myself breathing a little harder when I was on the bus today. It was an unusual feeling, which I never had before. Last month there was a gas leak and CO in the furnace, but it is out of my system. However, the residue under the lid of the stove still had residue of CO, so maintenance cleaned it up.. What causes this and what should I do. I don’t want to go to the emergency room again, is there something I can do to relieve this feeling?