Have you discussed this with your doctor? The funny feeling down your arm sounds a bit unusual to me and something to mention and see what they have to say. I know for me personally, I have been woken by some very odd spasms that I believe were related to my stomach or abdominal muscles. I had slacked off a bit on doing my situps and started to get the very odd spasms. I mostly woke up at the end of them but I caught one and it was just very odd how my whole stomach just spasmed like crazy for a second. Though I did not have any heart symptoms as a result but maybe something is going on with your stomach like gas or something and it is over stimulating your heart. In any event, I would contact your doctor to see what they have to say. The fact that it doesn't last may be a good sign but I personally wouldn't let any symptoms that shoot down my arm go without investigating a bit. Take care.