 I have had this problem for some time. Usually, when my friends ask me to have to a meeting with them for, say, doing a project with them, I get anxious for no apparent reason, sometimes I'll start worrying about the meeting days before it's going to happen. Even though I know that I will be able to do what is required of me, I still get anxious about things like not being able to do what they want, that they do not actually want me in and have just taken me in so that I do not complain, being potentially pushed around by my friends to do more than I should for the projects, among other stuff. It's got so bad that I get super anxious at a simple text even hinting at starting another project, my palms get sweaty, I get nauseous, I become uncomfortable etc. I even pulled myself out during the middle of one project due to my stress and anxiety. This doesn't happen when I'm doing projects by myself. 

What should I do? Is the problem with me or my friends? Should I just say "no" to every opportunity they give me? How can I ease my fear of group meetings?