Re: What is going on with me?
I'm sorry to hear that you're in such a bad place right now. I know somewhat how you feel having been there myself (not exactly how you feel of course).
I was seeing doctors about possible blood clots, holes in the lung, heart attacks, freaking out about cancer and went to ER myself once when I almost fainted and lost the feeling in my hands. Prior to all this things were going fine: I was confident, in a pretty decent relationship, enjoying my course at university etc.
I think answering "how do I convince myself I'm ok?" is a really difficult thing to do in some respects. TBH I am scared of giving you a bad/insufficient/poorly worded answer so please bear in mind that I can only speak very simply of my own experience which was far from a simple matter as I'm sure you know your situation is also not simple! I'm not a therapist and I'm far from perfect so please take what I say with a grain of salt.
Basically, my answer is that on one hand one of the best things you can do right now is come to terms and accept the fact that you're NOT ok. Will you BE ok? YES, but right now you feel awful and confused and are worried about what's going on so no, right now you're not ok and that is FINE. Not ideal, but it's ok to not feel 100%
It's great that you will be seeing a therapist soon because hopefully they will really help you to understand what exactly anxiety is and how it works and affects your body, personally one of the things that helped me the most was simply learning about what I was suffering from and learning to understand it. It gave me a sense of greater control (even though I really wasn't in control at the start, it helped lessened the frequency/strength of my symtpoms at least part of the time).
The other thing I was going to say which may sound like it completely contradicts my first point is to try learning how to tell yourself and believe it when you say "I'm ok right at this very moment", anxiety feels absolutely awful, but it can't kill you. Even if you feel awful, if you're still alive and breathing, I assume you are still doing things if you find you're having to leave class. Hopefully you're still showering and eating etc! If you're well enough to be doing those things you can honestly say that right at THIS moment you are ok and try to keep the future out of your head for a little while. It's a bit like meditation, just clearing your mind of all the worries and thinking about the moment: what you can hear, see, smell etc. I know this is very hard to do when you're suffering from anxiety symptoms and panic attacks but try to give it a go.
^ This is a very bad explanation of "mindfulness", if you want to try it out do some research on it to see if you can find better explained information on it than what I could give you. This is a technique my psychologist taught me.
Please know and remember that you're not in this alone, there are many people on this board who have been through similar experiences to you and are still going through them, and most importantly, many have come through that dark time stronger than before.
You will be ok in the future even if you're not so crash hot right now and there are plenty of people here you can talk to and ask any questions *hugs*