Long attacks aren't unheard of, but they are uncommon. An attack lasting days, as far as I've been told, is not possible. It's difficult for your body to remain in such a state for a long period of time - it's a lot of stress, and it takes a lot of energy.
I know for months following my diagnosis, I felt that every day was a battle. At the smallest of problems, I could feel my heart pounding. I would feel constantly trapped, and even had difficulty riding in cars. I had a fear of suffocation, and when I wasn't breathing right, or had trouble breathing, I would become very, very nervous - and find it even harder to breathe!
These aren't considered "panic attacks" though - this would be an Anxiety disorder.
After having my first panic attack years ago, I have become very observant of my body and of anything I might find wrong with myself. It may be that you are nervous, or are working yourself up into a state where these "symptoms" seem more than they really are. Like, when I found it difficult to breathe - and then wound myself up, until I made it harder for myself to breathe!
Chances are, you're worrying yourself into a frenzy for no reason. But, to ease your mind, go to the doctor. Make sure. It's perfectly normal to be frightened, and I'm certain that you're not crazy - you're just experiencing Anxiety, like millions of others.