The situations where you have your problems are all where the Total Lung Capacity [TLC] is slightly compromised either due to position or pressure. Generally this slight reduction is not noticable beacuse nature has built in some reserve capacity in our lungs.
Normal breathing has two components. Inspiration [taking air in] and expiraion [exhaling the air out]. Inspiration lasts slightly longer than expiration. In certain lung conditions such as bronchial asthma , chronic bronchitis, and Emphysema the bronchi go into spasm and though the person can comfortably inhale, the exhalation becomes difficult due to Lungs' recoil. Thus exhalation becomes not only difficult but more prolonged too.
With your smoking history it is just possibly likely that you have started manifestations of chronic bronchitis or emphysema. A consultation with a pulmonologist and a Pulmonary Function Test will settle the issue.
Dr Apurva C Madia
Consultant Cardiologist and physician