Welcome to our world.

First off you need to see someone and just talk it out. Go to a PHD or licensed therapist. Don't ever be ashamed of this. You need to realize there are millions of us out here fighting our own personal battles with this. Have you gotten to the point where you are angry that this keeps happening? You are not going to die and if you do you need to realize that there is nothing you can do about it anyway. See my issue what the same and for me at least, it came down to the fact that I wasn't scared of death but rather the process of dying. This was a a symptom of a bigger issue. I need to be in control OF EVERYTHING, but you can't control when you are going to die. See what I discovered in my sessions?
Now I'm at the point where I am mad that I get these attacks and wasted so many years of my life with worry, etc. I passed up so many opportunities that the thought of this sickens me.
You really need to talk to someone. Also, for peace of mind go to a doctor and have them do a full check up. Blood check, heart, lungs, kidneys, diabetes, etc. If everything comes back normal then you know it's all in your head.
You also need to force yourself to do things. small things at first. Take a walk around your block, go to a park with a notebook and write every little thought that pops in your head no matter how crazy/sad/funny/stupid etc. it may seem.
You will make it through this. No one ever said life was easy... Dont make my mistake and wait. I waited 10 years to do something. You reached out on here. There, that's your first step.
YOU ARE FINE!!!!!!!!
YOU ARE NORMAL!!!!!!!!
YOU ARE NOT ALONE!!!!!!!