What to do with the specific lap
The big understanding — about the locus — is slow. But in the very moment the loop has already started spinning, you need simpler things, and here they are.
First: name what's happening anxiety, not analysis. Not "I'm thinking the situation over," but "I'm anxious right now, and it's churning the thought." That alone strips the loop of its mask of useful work and part of its power. Second, the novelty test: "does this lap produce anything new?" If not, it isn't thinking, and there's no point continuing. Third, the calm-head test: "would I be doing this, acting this way, sending this message, if I were calm right now?" If the answer is no — set it aside; decisions from the peak of anxiety are almost always from anxiety, not from you.
Fourth — let the message sit. Wrote an anxious text — don't send it right away; let it stand till morning or at least an hour; almost always, by morning you'll send a different, calm one, or none at all. Fifth — postpone the worry. Adrian Wells describes this technique in metacognitive therapy. Set yourself a worry time — say, fifteen minutes at seven in the evening. When the loop starts during the day, don't argue with it; tell it, "Not now — at seven," and go back to what you were doing. By evening you often no longer feel like churning, and that's a lesson too: worry can be put off, it isn't as all-powerful as it seems.
And sixth, the most important: don't beg for reassurance. Two things are easy to confuse here. One clear question or request is communication: "It matters to me to know where we stand. If you go quiet for a day, send me a couple of words — it helps me feel calmer." You say it once, hear the answer — and live with it. Asking the same thing again and again — "you're sure you're not mad? and now? really?" — is quelling anxiety with someone else's word. That kind of reassurance soothes for minutes and feeds the loop: the more often you quell anxiety from outside, the more you cement that without an external "it's okay" you can't stand.