Panic attack lasting all day?

I've been stressed for weeks, seemingly just because of my surroundings, nothing specific is really bothering me. I'm apparently very susceptible to it. Today I had my first real panic attack where I thought, "Shit, this is it." I've never had one this intense before. Afterwards, I felt better for a short while, but then it got worse again. I was shaking, pale as a ghost, my hands were numb, everything hurt, I was derealized, dizzy, and in pain everywhere. This went on until the evening when I finally managed to calm down a bit. I think I'm afraid of the fear itself, I've always had it, but never to this extent. What do you do about it? Do they just come on suddenly for you, or do you also feel anxious and constantly on edge between attacks? It's like a constant "mini panic attack." I hear from many people that they don't have any real symptoms between attacks.

I'm afraid I'm getting caught in an irreversible vicious cycle.