I feel the impending doom feeling almost all the time, even when I'm not having an attack. I constantly feel like horrible things are about to happen. To the point that it makes me sick.
Usually how my panic attacks begin is with hyperventilating. I wind up breathing too fast and can't get full breaths. This then makes me panic more. Certain parts of my body begin tingling, mostly my face, hands, and arms. My heart feels like it's going to beat out of my chest. I'm nauseous. I can't move. I can't take deep breaths. I shake. I can feel my heart skip beats. I get really hot, red, and sweaty. The shortest I've had one (without medicine stopping it) was probably an hour. The longest has been three days. Waking up and going to sleep with a panic attack.
I'm not prescribed any anxiety medicine right now. So I take melatonin to try to calm me down. It kind of works. And I do the thing where you sit and describe everything you hear, smell, taste, feel, and see. It's pretty effective with the breathing aspect.