Diastolic dysfunction basically means that the heart isn't able to relax as well as it should, so the left ventricle doesn't fill quite as easily as it otherwise normally would. By itself, this doesn't usually cause any symptoms, especially if the systolic function (ability of the left ventricle to pump blood forward) is preserved. With diastolic dysfunction, depending on the severity, the body is sensitive to volume overload and can sometimes result in fluid backup into the lungs, resulting in (usually acute onset) shortness of breath. This can be exacerbated by high blood pressure. From what you are describing that your cardiologist said, your diastolic function is probably only mildly abnormal, and is unlikely to be the explanation for your occasional cough. The weakness and fullness in your stomach are also unlikely to be related, but that is hard to know for sure without examining you and knowing your fluid status.
I read your response and applied it to my diagnosis of severe cardiac microvascular dysfunction where my Cardiologists are seeing MVD patients with fluid retention problems and diastolic dysfunction.I am always pleased to read a physician's clear and concise explanation about a condition being seen more and more than in the past. Thank you.