Hi Phoebe
I get panic attacks. They first started when I first experienced cognitive dissonance in relation to JW doctrine. That was over 20 years ago. I also dream very vividly and I would have recurring nightmares about Armageddon.
I'm still a Christian and believe in Bible prophecy, but now that I have been away from meetings for sufficient time, and not had to endure the psychological propaganda of the WT, I don't have those same anxieties. Sure, I still get panic/anxiety attacks - but much more rarely now than I used to. And I still have bad dreams, but not arising out of the morbid fear that WT doctrine engenders.
A couple of things that might help in the short term if you have access to them might be to talk to a social worker, or someone else qualified, or to look into some CBT. The good thing about CBT - even if you have to pay for a few sessions - is that you can learn some techniques for coping that you can practice for yourself and improve at, so you're not on an endless cycle of treatment.
If you're still a believer (in Christ I mean, not the WT) then prayer also will be helpful.
In specific regard to the assembly and the hype reflected in the email you received, I can recommend reading this article:
http://beroeans.net/2017/05/18/a-fairy-godmother-religion/
I hope you are able to get some relief from your anxiety.
FG