In my twenties I had some years of severe panic attacks. It is funny, it completely dominated my life but I totally forgotten about it. Feel writing it off my chest, maybe it can help somebody.
For me they were hypochondria related. My vision would turn black, my heart would start racing and I got the feeling that ants where crawling from my heart to my arm. At these moments I was convinced I was dying of a heart attack or some artery was torn from my heart. Doctors would find nothing wrong with me, this increased my fear because it meant I couldn't receive any help. They attacks could last for hours, making me unable to sleep and mentally depleting me.
I have actually been close to death a couple of times for real. Once falling through the ice and once having a rare disease. These moments did not feel the same. Actually I was rather calm in these moments.
They attacks made such an impact on me that after a while I started being mortally afraid of having a panic attack. Thinking about it, thinking about my body, feeling the slightest discomfort in my body all these things would trigger another attack. Because of that I lost touch with my body. Worse thing was that I would sometimes wake up in the middle of an attack. This made me afraid of falling asleep. I would walk or cycle at night because I was too afraid to sleep. This made things much worse.
At one point I mentally saw the vicious circle I created for my self. I remember seeing it as one of those smoke circles some people make while smoking. I saw that my focus on this was what kept that circle alive. I saw that I simply had to stop identifying with it, step away from it. Almost magically the attacks have never returned.