I was diagnosed with CFS 6 years ago. At the time, among other possible causes, cardiac and pulmonary causes were ruled out. I've had trouble breathing and shortness of breath during significant exertion (walking up stairs, light jog, etc.) for all six years of having CFS, but lying down never gave me breathing problems until a couple months ago. Now lying down almost instantly gives me shortness of breath and makes breathing more difficult. My fatigue also became much worse around the same time that this started (again, a couple months ago). I'm seeing a primary care doctor to explore possible causes. My question is, can lying down exacerbate breathing difficulties in someone who has CFS and doesn't have any co-morbid conditions? Has anyone experienced that or met someone else who has experienced that? I know some other diseases are classically associated with this symptom (heart disease, liver disease), but I've never heard of lying down causing breathing problems in CFS patients. Just trying to figure out how worried I should be about a possible heart issue, or whether this could just be my CFS getting somewhat worse. Thanks in advance.