Hi there
the condition you describe will cause what is called mitral valve regurgitation.That means the valve to one of the chambers of your heart isnt closing properly and some of the blood flowing through the chambers can flow backwards. In lesser degrees it is relatively well documented in women over 55(dont know how old you are) and gives rise to few symptoms.You may experience a little light headeness and shortness of breath when lying down,but you shouldn't be getting acute chest pain i dont think.

You mention taking Zantac so i guess you are suffering with reflux or indigestion.Both these conditions can cause severe retosternal pain caused by acid and air getting trapped.There is also the possibility you could have a hiatus hernia which can mimic severe chest pain.I would say if your scans and x-rays of your chest are clear then you dont need to worry about your lungs.

whatever the cause,getting stressed will only make all the symptoms worse,so please try to chill out a bit until you see the doctor.