Did the EMT happen to check your blood Sugar
when you called 911? Panic attacks and low Sugar
symptoms are very similar. It reminds me of someone hypoglycemic eating high carb fast acting carbs and having a really sharp drop and when the blood sugar goes down too much (and not eating soon after), you start feeilng funny and at the end, the adrenal/cortisol kicks in, in order to raise your blood sugar and that could easily cause panic attacks. You said you hadn't eaten in a long time, and I am suspecting your blood sugar may be the culprit. Next time when you feel like that, eat something like a piece of fruit and wait 10 minutes and see.
My two cents,