What causes someone to feel short of breath when leaning back in a seat, even when their airways are clear?

Many possibilities: There canbe real shortness of breath or sensation of shortness of breath. How do you know your airway is clear? Obstructive things can cause this and you could need to see an ent for this. But other things cam cause this as well including reflux, cardiac issues,thyroid problems etc. if this is getting worse quickly see someone asap.