Huffing and puffing with light exercise?

I admit I am no candidate for track star status or athlete of the year....I have some junk in my trunk and a spare tire to boot. But I can normally walk the neighborhood without feeling like I'm about to suffocate. Anyone else feel like moderate exercise makes you feel like you are having a heart attack or need a ventilator?? I can't walk a few feet without feeling like my lungs are about to collapse...24w3d