When you are by yourself in your room or no one is home. ¿Do you make the same effort? ¿Or you tend to relaxe and just talk without thinking? Try asking a friend that your see confident and fluent. Ask him if he make "extreme effort and focus" whenever he needs to talk. Unless you had a neurological problem, it make no sense that speaking take such an effort. What happens to you (and us) is a conditioned learn behaviour. The good news is that it can´t be unlearn.