Are you on any heart medication? There are side effects with some ACE ihibitors and/or beta blockers. I had a dry cough when in an inclined position due to pulmonary edema as a result heart failure (chf). But with recent by-pass surgery, your cardiac output should be adequate. If not, blood backs up into the lungs and fluids leak into lung tissues and respiratior poroblems develop. Those circumstances ruled out it may be a respiratory problem.