This is a panic attack, I have the same thing, sometimes it happens to me when I jump, my heart starts beating super fast and my left arm feels tired and it hurts a little bit. Had a visit, kept this device on my body for 24 hours but nothing, they said I'm all right and super healthy. Last time I had one was 1 week ago. You should go at your doctor, he/she will help you.
i have the same thing when i have high anxiety or a panic attack ill stand up and cant breath or even walking a foot or two. best thing i find is to close my eyes and take a slow deep breath, and do whatever i can to get my mind on something else, drink sips of water. there might be a hidden reason why its going on, our body remembers things, places, events that we dont even think about or dont realize it impact it had. try stress balls, playing with a pen or something to for the mind and body to focus on.
There is a good possibility you are having a panic attack but because you have not been evaluated, you should see a doctor right away. An urgent care or emergency room would be a good idea to make sure that this is an anxiety issue and not a coronary event. We wish you the best.