@SassylovesbooksIt’s not a lovely idea if it’s not something the OP actually wants. I’d hate a surprise party and it would make me feel worse than having no party.
I would be speaking to my DH and explaining that, as he knows, I don’t enjoy parties and that he needs to cancel it. It will be awkward for him, but that’s his own fault for not thinking about what I would want, given it’s for my birthday.
Previously I would have gone along with it and had a birthday party that I spent time worrying about then not enjoying, but I’ve come to the realisation that sometimes you need to put yourself first.