I used to suffer from panic attacks day and night. Terrifying. I understand what you are going through.
I hesitate to post this for fear of coming across as some kind of crank, but here we go:
What worked for me: a diet of healthy animal fats, meat, fish, vegetables, minimal fruit, and some nuts. Basically, a blood sugar lowering eating plan with minimal carbs. No bread/rice/pasta/root vegetables or sugar.
I know it may sound insane, but that is what helped me. 9 years ago. Once the attacks stopped, they never came back.
My eating is not as strict now, but I monitor my blood sugar levels. I try to eat protein before treats to slow the release of sugar.
Recently I was at an exhibition of an artist who is epileptic and her description of what she felt when an unavoidable fit was coming on was exactly what I experienced with panic attacks. And then I made the connection! The ketogenic diet was originally recommended as a way to help people with epilepsy. It wasn't about weight loss.
So as insane as this may sound, you might want to try eating a ketogenic diet )or as close as possible) to stabilise your blood sugar.
I really hope you find help out of the panic attack nightmare. 