I Am A Women, 69 Years Old. Healthy, Only Take

I am a women, 69 years old. Healthy, only take simvastatin. Previously I have had my heart pounding so loud I couldn't sleep on my left side. Dr. checked it out (cardiologist). Found nothing wrong, told me to take Magnesium. It did in fact help. Until last night when My heart was beating so loud it was shaking my left arm, left side, left leg and throbbing in the left side of my head. It was not beating fast or slow just loud enough to shake my whole body. I was not short of breath, no pain, light headed or any other symptoms. It finally went away after several hours.???????????