What Causes Feeling Of Heart Beats While Standing With Normal EKG And ECHO?

Hello, When I stand up, my heart beats faster and I can feel it for a few seconds after laying down for a long time.. But when I stand up more controlled instead of sudden and fast, I feel that less or dont.. Besides that I can feel a pulse sensation around the body usually.. I have these for years though.. Focusing to it makes you feel it more I think.. I had been to cardiologist.. blood tests such as cholesterol and general check up.. an echo of the heart.. effort ekg test.. physical examination were all normal and heart in a good condition.. I often feel anxious and suffered from panic attack in the past.. thanks