Two factors you mention cause me to think that it is very likely your problem is not
cardiac but rather most likely muscle/skeletal in origin: 1) your age, 2) the pain seems positional
, that is it goes away when you change position...there is the possibility you may have a hiatal hernia which is aggravated both by smoking and laying flat, but I am inclined to believe, just on what you have told us, that your symptoms are Thoracic Outlet Syndrome type thing--laying on your side, your subclavian and other arteries are "pinched" obstructing proper circulatory flow, nerves are pinched, compressed, etc. TOS can aggravate the perianginal nerve that runs across the chest, causing "angina", etc.
All of this said, it should also be said that most heart attacks occur in the early morning: so definitely you should have a complete cardiac workup, with family history in mind, but I would also definitely have an UGI to check out possibility of hiatal hernia, and be examined for TOS....I placing my bet it's TOS, in which case PT would be a choice of therapy (a delightful therapy which most likely will cause the extra 15 lbs. to be effortlessly lost! I lost 15 lbs without realizing it just doing the excercises--didn't realize it until the PT reached to hold up my jeans which were beginning to fall down from being loose!
) Good luck! Don't ignore the symptoms, but hopefully I'm right.