BINGO!!!
You've hit on it EXACTLY. The reason I prescribed writing to friends and relatives is to get your mind into the HABIT of writing automatically. You shouldn't even be thinking about the physical act of writing. And I can do the reverse. I can actually get someone so self-concious about walking that he can barely walk. That happens to me when I starting thinking about all the muscle movements and commands sent from the brain to the leg muscles via the nerve system. Oh, and have you noticed how tough it is all of a sudden to breath? Just think if you don't CONTINUALLY breath you suffocate. Think about that air going in and out of your nose and down to your lungs. Yes, what was once a simple act that you took for granted is now becoming very difficult to you. But not to worry. You have been breathing automatically for so long that you will revert to that process soon. Well, the same holds for writing. You should write AUTOMATICALLY with NO self-conciousness. That is all I do when teaching folks how to avoid writer's block.
It's been a long time since I suffered severely from this problem that I have almost forgotten how DESPERATE I used to be when I had Writer's Block for MONTHS at a time. I even thrashed around on the floor and prayed for the Writer's Block to go away. No answer to my prayers at that time...until months later I heard something on the radio that taught me the first of my techniques. Then I started to write one article per week without letup (and my first story was read on the radio!).
So for those of you out there really suffering from Writer's Block, I know where you all are coming from. After I learned the initial first step on overcoming Writer's Block I undertook vast research and mental experimentation to learn the techniques of overcoming Writer's Block. I sort of looked at myself as a Thomas Edison using my mind for experiments in this area. It took about 3 more years before I discovered almost all the techniques I now use.