It sounds like anxiety attack. I had a bout like that for about a year when my grandfather was dying of leukemia. My heart would beat so hard and fast you could literally see it beating through my shirt. I would suddenenly feel weak, hot, heavy feeling on my chest, hard to breath, I would turn pale. I went to mayo clinic as I thought something was wrong with my heart. Turns out I was just panicking. They told me to relax. That's it! Once I found out there wasn't anything wrong with me I was gradually able to overcome it. I would do deep breathing during an attack and tell myself it was only anxiety. It worked cause I haven't had one since. I can feel one welling up every oncein a while but I always am able to stop it now.