Social anxiety disorder is the third-most-common disorder in the US... so, yes, it's very very likely that many other people have that exact same experience. You are not alone! Whether you have the actual social anxiety disorder or just have anxiety about posting on forums, it's certainly a very common experience. The best you can do is just step out and try things, and remember that everybody messes up and it's okay for you to mess up; and that being judged is something that has much more to do with the other person than it ever has to do with you. The more practice you get, the more confident you'll get, the more you'll feel able to step out and get more practice, and the better you'll get at communicating. Keep doing things just a little outside your comfort zone--just enough that you can do them with only a little bit of nervousness--and you'll get used to it. It's kind of like you're teaching yourself that "talking to other people isn't actually as threatening as my brain is telling me that it is". Just another kind of learning, really.