My heart beats really fast and I feel it's going to jump out of my chest and shake really bad and I can't stay still and I can't walk so what do I feel like i can't stay still and I just try to do breaths in the short breaths and slow and it hurts my chest really bad and my back I don't know what I have, they say its a panic attack but I mean I have nothing to panic over it just happens of the blue im really scared i dont know waht i have, thank you please help me