What is an anxiety attack?

This might get a bit long, please bare with me.

So yesterday morning I woke up with a weird pressure in my chest, right in the middle. I kinda felt like someone was squeezing my heart. It kept getting worse, and I ended up going to the ER. They tested for heart attack and blood clots, but couldn't find anything. 8 hours later I was discharged. By the time I got home I was extremely dizzy, felt weak, especially in my shoulders and arms, I had trouble breathing, I could not stand on my feet because I felt like I was going to pass out, to the point where my vision was getting all funky and my ears were kinda closing up. It was BAD. So I found a friend to watch the kids and called an ambulance, and shortly after midnight I was back at the ER. About an hour and a half after I had left there.
They did another EKG and some more bloodwork, again, nothing. Meanwhile the pressure was getting almost unbearable.
So that doctor, and the nurse, said it's probably an anxiety attack. They gave me Ativan, which didn't do anything. The doctor also said it could be Asthma and gave me a nebulizer treatment which, again, didn't do anything. I KNOW it's neither one, but on the discharge papers it said Acute Asthma and Anxiety. I know they're just running out of ideas, which is why they told me to follow up with my regular doctor and get a referral for a Cardiologist.

So, my question. I have never had an anxiety attack, so I don't know much about it. Is it even possible for an anxiety attack to last three days? (it's going on three days now) I thought they come and go rather quickly? Also, is it possible to have an anxiety attack without being anxious about anything? And, shouldn't have the Ativan helped if that was really it?

The first doctor I saw didn't say anything about Anxiety or Asthma. He didn't check for that either.

All I know is that the pressure is still there, the dizziness, the weakness, now with headache and cough. I just want to know what's going on!!

Anyway, thank you for reading all this, and for any advice you can give me.