What Causes Breathing Difficulty At Night While Sleeping?

I have been diagnosed with diastolic dysfunction type 1, which does not sound very serious. Yet I experience breathlessness when in bed at night, just lying still. I have even been woken up trying to breathe. Sometimes I have to chose between eating and breathing. I often feel as if I am suffocating. I am now on Beta blockers, diuretics, blood thinners and blood pressure tabs and am able to go for an hours walk each day plus some gardening. My GP does not seem very interested, not even enough to track down the cardiologist reports of test findings. Am I as ill as I feel or is it all in my mind?