i went to a cardiologist to get an ECG and everything was normal for my heart, normal size of everything, the only thing is that when i breathed deeply i started to loose feeling in my extremeties and when I was just laying down, breathing normally during the test, my heart rate was 48 beats per minute. Is this normal? the cardiologist recommended a 24hr holter but I have had these tests before with the same results. Any suggestions on what i may have?