Its natural. The most import thing to remember is that it happens to most people. The fear of making a mistake, looking like a fool, or suffering consequences, are common among performing artists. It most likely will always be something you'll experience, accept it; some embrace it and use it to their advantage. The body and mind are connected, know where the tension is coming from. Are you experiencing physical tension or mental chatter, or both? The body is the subconscious mind. What is your body or mind telling your Inner Artist? What is your Inner Artist trying to say? Which is correct?