My father was diagnosed with lung cancer in December of 1983. He was 69 years old at the time and had been a heavy smoker for 50 years.
He was helping someone unload a piece of furniture from a pick-up and became short of breath. In his words, he "couldn't catch his breath."
This episode worried him and my mother, so he soon went to see his doctor. After looking at my dad's x-ray, the doctor told him he needed to see a specialist and not to put it off. He told my dad that if he waited 6 months, it would probably be too late.
My dad was one of the lucky ones. He had one of his lungs removed and needed no further treatment. My dad was with us for another 15 years. He never smoked another cigarette and spent the rest of his life trying to convince others to stop smoking.
From my experience, what I want everyone to know is that if you feel something isn't right, there's a good chance that you are right. Go see your doctor and DON'T DELAY. Early detection gives you your best possible chance. And PLEASE don't smoke. If you do smoke, please stop.