As for me (I hardly know anything about your condition, so I'm just sharing my experience with writing texts), I have noticed that writing a certain text (a blog post, a presentation of some code or scientific idea, or whatever) is becoming an ever more intimidating and unclear and anxious-making task for me the more I try to finish the text sitting alone in front of a computer or a piece of paper. I hoped that it's a matter of experience, but it doen't seem to become better the more texts I write.
Becoming more free in the physical space (e.g., taking a walk) makes me a bit more free and clear in my mind, so that I can better and clearer express what I intended to express. The freedom feeling eases a bit the anxiety.
But the most helpful thing is commnicating with someone. If I go and try first tell something in a very free informal manner to someone, then writing it down immediately after I successully communicated the idea to someone can be perhaps 1000 times easier and faster than writing it down just sitting in front of the computer without actual lively communication with people on this topic. Just don't let the encouragement the insteresting communication has given you go away, don't distract yourself to other topics, write down the essential thing.
As for me, I also say to myself and it helps: Don't try to write something complete and perfect in all the aspects of your intended text. First, express the main idea the way you would tell it to someone, and don't be anxious about the imperfectnesses. Then, calm down, look at it once again, re-read it, and go on extending it: add some missing references, notes, some side ideas. Then, perhaps, you might want to expand on some of those "side" ideas. Then look at the text as a whole once again, calmly. Give yourself freedom to imagine how the text could become better (I can't really conciously control my creative activity in thinking and imagining, so it's better not to try to direct oneslf, not even to have a strcit plan or think about a plan, but just feel free and not anxious); perhaps, restructure it, beautify, add illustrations, think of some concept that would go through your text and help organize the presentation so that the text will be more clear and concise to the readers, without involving any distracting, not really relevant notions.
The wiki way of doing small edits step-by-step, ever improving the text helps me a lot. I'm not anxious anymore about it being imperfect: I can return and edit it and extend later. It's much more important that it can be useful to the readers right away, rather than that it is not perfect yet. This idea helps me calm down and lower my anxiety.
I find it unfortunate that one often has to prepare something written down to present one's ideas at scientific seminars, because it's so hard for me to write something clear when I'm alone, and so much easier to write something down after you already have discussed it (at a seminar). It becomes a circular problem: to write something down, I have to discuss it before; to discuss it, I'm supposed to write something down--the thing I'll present at a seminar.