Calming

I 100% agree that you should talk to a doctor about this.
Doing a first look and doing a ceremony rehearsal the day before will probably help some. I find yoga to be pretty helpful, I use and like myyogaworks.com , because I don't have to go anywhere to do it. They also have a lot of mediation classes.
Another thing that helps a little bit (especially if combined with yoga and/or breathing exercises) is these relaxing candies. This link is to the company's website, but I just buy them at Whole Foods or Wegman's.http://www.bachflower.com/bach-rescue-pastilles/

I think it's best if you talk with a doctor about this.

They can help you decide what your best treatment could be. Start off with breathing techniques, to therapy, to medication. If your anxiety is bad enough to disrupt your life, I don't think forums are going to help you - but doctors can.

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I also have a shortened PR interval and have panic attacks. I would definitely talk to a doctor. There are a lot of medications out there that can help with arrhythmia and tachycardia, or it might be something more serious. There are also certain things you can do to control your heart rate when it's skipping, but I'm not going to give any specific medical advice via the internet. In spite of the similarities, (and I got really nervous right before my ceremony) I have never blacked out. I honestly encourage you to speak with your primary care doctor.