Imagine if in your regular life you regularly walked into shops and tried to ask for something, but everything that came out of your mouth was incoherent nonsense, and eventually you had to say "Bye!" mid-sentence and abruptly walk away in front of the stupefied patrons. For most people, this would be mortifying, anxiety disorders or no, but that exact thing happened to me countless times when I first left the soothing embrace of the Anglosphere long-term.

At first I'd get cold sweat and shaky hands just buying a bottle of water, but I had to tell myself "Go! Do it! If you fail, just put it behind you!" - after a while I didn't even feel embarrassed by communicative collapses. I'm not a naturally thick-skinned person - I had to force myself to build up a tolerance for awkwardness, because it's an inevitable part of language learning when you're in a foreign environment.

Life in a language you're not comfortable in simply isn't the same. Your humour, intelligence and overall competence become a fraction of what they actually are. When learning a language, it begins as a goal, then becomes a tool, and only last becomes a means of self-expression. If a beginner expects self-expression from the very beginning, they're going to be very nervous indeed.

I know it is a bit ironic, but I am a mental health professional and more than 80% of my clients have anxiety disorders of one variety of another.  Brain scans and research shows that some people are biologically more predisposed to anxiety than others.  I also happen to have spent much of my first five years alone with my chronically depressed and almost deaf mother for 6-8 hours each day. An environment with far less social interaction and less talking than most children are raised with.  Not surprisingly, I was a shy and quiet child, who gradually learned to be less inhibited about talking to others. 

Social anxiety inducing situations do not help you relax at the time, but the process of not avoiding your fears and gradually having some success does eventually reduce the social anxiety.  I actually have very little overall impairment from social anxiety in my life now after years of confronting it and learning techniques to manage it in my everyday life--- as well as teaching those techniques to others.  In English, I can manage the situation just fine and people I know have even argued with me about my belief that I am an introvert-- because I do not appear to be to most people. However, the process of learning a second language has shown me that my predisposition to anxiety is not entirely gone--- I can and do overcome it- but trying to speak in a language that is not yet habitual for me exposes to me that my brain´s propensity to anxiety is still there.  

I had the same issue as a tennis player.  At the first of each season, I played better in practices than in competition.  It took a few months each year to get ¨tournament tough¨ under high pressure.  Many other players tended to have problems with motivation during practice and then the competition helped them to play better.  Everyone has an optimal level of anxiety for performance.