I don't think you are alone among aspies in regards to feeling constant anxiety/fear and so on. There are a bunch of things that helps me tone it down, including meditation, playing music to the point where I am totally wrapped up in it. My work, when there is a crisis, ironically, is also when I become very calm and just do the things that have to be done. I think the anxiety recedes during a crisis in an area in which I am competent because I know what to do and just do it.
What has been the most successful for me is a bit tricky to explain, but... the anxiety doesn't disappear, but it doesn't matter. Now that I think about it, it is a bit like the chronic pain I have. Basically I am never free of pain, but most of it has gone to background and does not particularly affect me on a day to day basis. Kind of like the noises the refrigerator makes...it is loud and bothersome (our current frig is a noisy sob), but even that noise goes to background.
And if the anxiety is so high that none of those work, I nap until it gets better again. 
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The river is the melody
And sky is the refrain - Gordon Lightfoot