Fear of elevated hear rate?

Kay so this might sound kinda strange but I'm really scared of when I can feel my heart beating such as during exercise. It makes me really anxious which of course just speeds it up more and then I feel nauseated and can feel my heart beating really loudly in my head and it makes me feel like I'm like dying.... Like what is this? Do you guys know anything that can help? I try to just like breathe and calm down but it really doesn't help.