I don’t want to go to the wedding

Thank you all for your replies. They are very reassuring. I’m not sure yet about going to the church as i know I’ll have to continually explain to others why I’m not going. Maybe too stressful.
It’s good to know I’m not alone in my way of thinking. ?

I felt the same a few years ago when invited to my Friends golden Wedding celebration.
It was a very big affair, marquee, cateres etc.
My H had Alzheimer's and I didnt want to go on my own, too many memories and too many acquaintances.
I explained to my friends and they "sort of" understood.
I sent a generous checque to a charity of their choice and my friend took me out for lunch a couple of weeks later.
Now, at my age, I will not do anything I don't want to or know I will be uncomfortable ,trying not to hurt feelings though.

Yes Mande, I can empathise with you. I too am not fond of big weddings or parties etc , but for a different reason. I am divorced and my ex-husband and his wife are usually invited as well ....it's always awkward for me and no one understands.
In your case, you have a very valid and distressing reason (your medical condition) ... if she's a good friend she will understand. You can visit the couple, when convenient and wish them well, personally . Good luck xx

Sort it quickly - give your friend time to invite someone else in your place

Of course your not being unreasonable. It is up to you whether you go or not. I completely understand how you feel and I wouldn’t go in the circumstances either. Unfortunately your friend may be a bit upset at your stance, but if she’s a real friend she will understand when you explain how you feel.

Could you attend the church service but not the reception?
At least in the church it will be calm and with an order of service. A wave or quick hello to those you know and take your seat. You can slip away quietly while photographs are being taken.

Can't you just go to the church/registrar office bit? Explain to your friend that you would love to see the young couple actually wed, but you really don't like big dos. Give them a really nice present. That will make up for a lot.