Right now, I feel my heart beating really fast and I can feel it through my skin (which I normally can't) and it feels like my throat is constricted, and it's sorta hard to breathe. This isn't the first time it's happened, and I've also gotten really strong pulses in random places, ex. high on my forearm, or on my knee or upper thigh. These things don't happen when I do physical exercise, only when I'm sitting or laying down. Should I be concerned?