Yes I have long and intense panic attacks as well. I have periods where I am constantly shaking and overbreathing and have multiple panic attacks. I have learned more about what triggers them but I still can't quite control them.
I also experienced the same thing with therapists. Many only know about panic attacks from their books and it seems they don't believe their patients. What would be helpful is if doctors/therapists would accept that textbook cases and real life cases are very different. Each and every one of us is different.
In my case I felt stigmatized..because I had anxiety, I often wasn't being taken seriously. One doctor told me that in my imagination my panic attack lasted one hour when in reality it only lasted 20 mins, because one can not be in panic mode longer than 20 mins. I told him no, it lasted for the entire duration of a train ride - hence one hour - but he still wouldn't believe me. The same thing applies when it came to explaining the intensity of the panic attacks.
Its one of those things you can only understand when you experience yourself. It would be great if more doctors were compassionate. I don't expect it but it's wonderful when someone tells me he/she understands and takes me seriously.
I hope you can find a way to relieve some anxiety. Maybe you could try another doctor who is more understanding.