I wake up with a shivering sensation.

Hello Doctors, I am taking Cardace 1.25 in morning and Dilzem CD 120 in night and my BP usually remains under control, I atleast check is twice a week. However, in past 3 years I have had 5 ecgs, 3 echos and 2 TMTs that all came normal. last year I had a TMT that Doctor said was quite good. Problem is I wake up in the middle of the night feeling a bit pressed for breath or a mild shivering sensation and that odd feeling. I had consulted a cardiologist last week and an ECG done that came normal. What do I do for past 5 years or so every year, Doctors do ecgs/echos and it comes normal but this problem doesn't go. Can I have a heart problem and still all ecgs/echos and TMTs are coming normal still? Do I have some rare problem? Please help. Last doctor also wanted to change my BP medicine which I am taking since 4 years. Is it ok?