There are lots of medication options for anxiety, so hopefully your psychiatrist will have a solid long-term treatment plan that will work for your difficult child.
I grew up with a dad who suffered from panic attacks, and he was rx'd clonazepam among other things, but it made him too disinhibited (scared my mom to death to be riding in the car with him -- his driving became way too erratic). I'm not sure what else he took over the years, but I know his panic episodes would strike out of the blue. They later determine he is agoraphobic. He never was able to go to any school event I was in, and absolutely avoided crowds at all costs. If we went anywhere, he had to know his escape route ahead of time or he just wouldn't go.
The way panic attacks were explained to me, sometimes the underlying anxiety is often a state of mind the person is not even aware of. They tend to just ruminate over stuff until things build to a level where the mind tells the body to just shut down because it perceives itself being on overload -- so much so that the fight or flight response kicks in and everything goes haywire. It's like being born with an over-sensitive startle reflex.
My difficult child 1 had panic attacks whenever we'd go for blood draws. True needle phobia. He acted as if his life were about to end and tried to negotiate ANY other means of getting the blood -- can you just cut me? can you just cut my arm or my finger with a knife? -- rather than be stuck with a needle.
Lexapro was the magic bullet for his anxiety and he now tells me to wait in the lobby while he goes into the lab himself
He still has problems feeling overwhelmed in crowed places, especially if it's a new place and he doesn't know anyone. We went to a charity event today, and although he knew some of the kids there, he sat silently most of the day playing his gameboy (his way of avoiding/escaping). He admitted to me feeling a bit overwhelmed later this evening, so I need to think about whether this is a problem that needs to be addressed.
My mother, on the other had, cannot take Lexapro -- makes her very wired. Celexa works better for her.
husband takes Paxil for his anxiety and it really seems to help him a lot.
I take Norpramin (desipramine -- a tricyclic) for my anxiety and it has worked much better for me than the Celexa I started out on. I got flack from my GP for it because it is such an "old" drug -- meaning, it's been around forever and there are so many other "new and improved" drugs out there. But he can't change my mind because it's still working for me, and it's been about 7 years now. Hard to argue with that.
Hope your son gets some relief for his symptoms soon. That's a hard thing to deal with even for an adult.