Innately Habitual Defence

Most people will know me as rather chirpy, energetic and hyper. Most of the times, I can't even differentiate if I'm doing this habitually or if it's innate. After all the hype, I'll usually deflate when I'm all alone or whenever I'm with people I'm entirely comfortable with. Walls of defence are usually up without any specific intention to do so but supposedly it's a natural human defense. I'm not even sure if I've got a wall around me now. What's second nature?