I had a tight chest and that sense of not getting air. Ended up, at night, I try to lie down on my back without a pillow to expand my lungs. When I got it during the day, I realized I was getting really hunched over, so I tried actively to get my head up and straighten my back so my ribs could move. I know it sounds sort of military, but it really made a difference. I am not sure what caused it, but the only solution for me was physical. Having said that, I went to the doctor about my heart and had it checked out, before all of this.
So, see your doctor if it is bad, because we just don't really know the causes of these things, though we can guess.