Hang in there, it does get better as time goes on. Yes, it's most likely all mirena caused. Some of us just take a lot longer to recover. I'll be 6 years post in May, and I feel pretty good almost all of the time now, but it took me to the 4 1/2 - 5 year mark. As time goes on, you'll notice fewer and fewer panic attacks. One day you won't be able to remember when the last time you had one was :) Some things that I do to keep mirena panic attacks at bay are to eliminate all caffeine, limit alcohol, keep my vitamin D levels up, keep my thyroid levels from being hypo, rest when I need it, and get plenty of exercise, even when I don't want to. Hope this helps!
-nile