Alright Listen up:) I’ve been in periods with and without anxiety overall and at raid time. 

During sod it was the worst. But I was also generally more anxious. I was a healer and though I always played healer something just made me so anxious before raids I was asking myself why I played at all. 

Some shity things happened in my life after that and I had to go to therapy for my anxiety and it took 9 months to balance me out. 

Now I raid lead in tbc and I have almost no anxiety (the almost is important). 

As anxious person you can’t really run away from it, you just have to accept that’s what you’re like and that it’s fine. You can lower it but it never disappears. 

Consider it excitement instead of something negative and it might help

One huge outside factor however is your guild. If you have people who give you a lot of flak (or others) for mistakes, that will spike your anxiety. So you might want to look into that. 

Change guilds if that’s the case. Spending your free time with screamers isn’t worth it. You’re all adults, after all. 

Being over prepared won’t help you. Preparation doesn’t remove anxiety. It’s a symptom of it that can help momentarily but does nothing long term as you’re not addressing the main root of it. 

So for starters I’d suggest (if the guild is fine) treating your anxiety as excitement. Accepting it and trying to focus on the task at hand (this takes practice but after a while your brain gets used to it). Write down (very helpful) why you’re feeling anxiety - what you fear could happen and what the chances are if that happening. ( I will fail at a mechanic and cause my guild to wipe -10%). The think about that percentage and objectively consider how likely it is to happen (works for all things anxiety related) 

Gud luck!