Scared

So I was in my English class today, and it suddenly hit me. This massive wave of anxiety, my whole insides clenched and ached and my hands and legs were shaking. I could hardly breath and my heart quickened so fast. My friends took me to the nurse and then left me and while i was explaining it just all tumbled out, all my problems, my self harming everything. She’s booked me in to see my college counsellor but now I’m terrified, I don’t know what to do I’ve never done this kind of thing before, can anyone give me some advice on what therapy is like?