why is my heart beating so fast?

Why is my heart beating so fast? Is this like what they said? Like love? Is that it? I don't know, I am not sure.... They said that love makes your heart beat fast, faster than it usually was. They said it will make you happy, excited or whatever. I am not sure about this... Neither do I feel excited or happy. I feel down, for absolutely no reason. I can't explain. Am I hurting? I shouldn't, right? This doesn't feel like what they said. I feel very different. Should I be concerned? Am I dying? I don't know....