you can feel your chest beginning to tighten as if your being squeezed by a hug which makes you short out of breath or even just pain in the chest, when you automatically out of no where feel dizzy or fatigueness, nausea or vomitting, when ur starting to sweat a lot for no reason, when you feel like you heart hurts (aka heartburn), when you feel like you cant breath well like shortness of breath or heavy breathing, jaw pain, and back pain.