I'm sorry you are having this experience. I've had that sensation of racing heart. Like I can't calm down. Honestly, what helps me is to deep breath (breath in deeply for a count of three, hold for a count of three, breath out slowly for a count of three, hold for three, repeat). This is calming to me. And while you do it, visualize something soothing (whatever is to you like a beach, a field of flowers with birds chirping, etc.).