My son who 23 years old is having a racing heart with heart rate up to 130's. He says he feels like it is hard to breath during these episodes of high heart rate and that he doesn't feel "right". When his HR comes back down to 80's he says his heart feels heavy. This is the second time in a week it has happened. The first time he went to the ER. They did an EKG which was normal and he had blood work done later that was normal. Sometimes he says his heart feels like it "jumps" . What could this be and is it life threatening