how do i tell my family

My family and I are leaving the country for vacation tomorrow, but I'm really anxious to go. I'm a very anxious person and I tend to avoid things that scare me, which I know is bad, but this time I really, seriously don't want to push my limits. I think I enjoy traveling, but on my own terms and preferably not with my family. I don't exactly get along with them, though we have been doing better as of late. I'm afraid to upset them, cause things will get awkward and I know I'll strain our somewhat improving relationship. Going back to my original question, how do I tell my family that I don't want to go?

This is quite urgent, so I appreciate any and all advice.