I am so sorry that you are having such horrible experiences. There is really no practical way to glean what might be causing the physical symptoms and anxiety.
Have you experienced some type of trauma, perhaps? I have been attempting to manage symptoms of PSTD and what you are describing sounds very much like a response to trauma.
If you feel that you you are on the edge, please, call your local mental health hotline. There could be many reasons that you are having such dramatic symptoms and anxiety. Try to keep in mind that this is a serious challenge and it may seem hopeless right this minute. But, you CAN sort this out ~ this is temporary and things will get better.
My most sincere best wishes to you and brightest blessings.