Make it so your decision isn't essential to your self-image/ego/self-concept. The anxiety comes from the fear that the decision will lead to you creating an unacceptable or inaccurate self-image. Being an INTP, your Ti-Ne can really make this difficult. You announcing your decision to others is you attempting to broaden your self-image through association with others. They are our mirrors and essential to our maintenance of our self-concepts. In that sense, you announcing your decision, makes it more concrete in how it could impact your self image.
How do you make your decisions less anxiety-inducing? You can do that by lessening the importance of your self-image/ego/self-concept or by treating the symptom of the resulting tension. In my opinion, mindfulness meditation is a really good option for the former. You could also attempt lowering the bar as prior posters pointed out by not caring, but you may find yourself caring sometime down the line in the form of it being a regret. If you do not value having, at all times, a sharp mind, Valium is good for treating the symptoms of the anxiety. Therapy may help you learn more about yourself, what you value, be more acceptable to yourself, etc., as well. That, or as some poster may eventually point out, you could just grow a pair, which, of course, is mostly worthless advice.
Western society has a lot of options to reduce such anxiety, but the underlying values of that society make it difficult to maintain.