Yea it was happening to me and whenever i smoke my heart feels fast but most of the time when im laughing i just forget aobut it and ive sort of gotten used to the feeling. If u just chill out it actually feels pretty good at times cause ur chest feels relaxed and numb sorta. But yea i understand why it was freaking u out cause it did for me to but just try to chill and get used to it cause it wont be as bad.