I had them quite frequently in college. Various things would set me off, being in a movie theater, long (4 hour+) drive, etc. etc.
Then I cut caffeine out of my diet. Have not had one since. No medication, none of that, just drop caffeine completely.
I can relate to the going to the ER however, i'm asthmatic and as soon as I had one I would feel as though I were having a asthma attack. Spent a
pretty penny for nothing. My main concern at the time was since my panic attacks had very similar symptoms to a heart attack that I would start
ignoring them and when I got older end up dying from something I could have prevented. That didn't help matters much.
Come to find out my father also had them around that time in his life. I notice that a good percentage have them in their late teens and early
twenties. I wonder if it's not possibly hormonal in some nature, couple that with the stress of going to college or moving out etc. and you've got a
pretty rough situation.