I have never heard of it happening in daytime.

The difficulties of breathing that typically occur with autonomic dysfunction are usually secondary to heart and/or BP related problems. Like shortness of breath in exercise because the BP drops and heart rate increases...which in turn cause shortness of breath.

Your pulmonologist should be able to determine if your breathing is autonomic related to other cardiac problems...or a problem of it's own.

Do you notice any other symptoms when you are short of breath...like your heart racing or lightheaded?? Have you taken your BP and heart rate when you are experiencing symptoms??