Hi. I'm a 19 yr old female. For about 3 or 4 years I've been having this problem. First I feel like all my blood rushes to my head &I get light headed &feel "butterflies". Then my heart starts beating fast. I don't just mean fast as in just ran a half mile but probably double that. Like 7 or 8 beats per second. You can see my chest beating. I've had other people feel it as well. It also gives me very sharp pains in my chest. It hurts to breathe or swallow. It feels like there is a truck tire sitting on my chest. Then it just stops. Not gradually. Just instantly stops. This happens very randomly. I could be working or lying down or folding laundry. I've been to the hospital multiple times&they've never found anything wrong. I need to know what's wrong.