I understand you just fine. I'm sorry you're having this trouble with your family. They are disrespecting your wishes and invalidating your needs as well. I am an introvert with anxiety and I like to be told in advance what the plans are because I too need time to prepare myself. You could try approaching the most receptive family member and explain your needs. You're not selfish and you're not alone. I'm here if you want to talk. Good luck with your family.