Hi @Confused93, I suffer from anxiety, too.
Please, for your own good, can you take someone to the meeting with you as a support and as a witness to what is said to you by your boss? A union representative would be ideal, but any reasonable adult would be fine.
Your boss cannot fire you for taking sick leave!! It just isn't legal.
Perhaps even call the Fair Work ombudsman for some advice on this.
It depends a bit on the job and what they are like there- but they will have to try and come up with a legitimate, legal reason to fire you. If they are smart, they will have sought legal advice on this.
Also, your boss has no right to ask you to come in while you are on sick-leave. You might be best to tell them you are too sick to come into the meeting and get a doctor's certificate to prove it. Or get someone else to call up your boss for you, so you don't have to personally speak to them at this time.
If you are so stressed with anxiety that you are feeling physically sick, then you are clearly not up to attending a meeting. To do so would not be in your best interests.
I am no expert but I have been through the whole thing- dealing with ruthless, unreasonable employers and going to the Fair Work Commission to argue my case.
I hope it all goes well for you... but remember you have rights and you are entitled to your sick-leave.
Please let us know how it goes.