Thanks, I looked into ACT briefly many years ago forgot about it. Is this the book you are recommending?
I think that the insights you find, and that you guide your client to find for themselves, are going to come from your theoretical orientation and case conceptualization.
The insights you and your client come to, you'll get to by different paths, depending on the theoretical orientation you're coming from. It'll be different coming from a contextual behavioral versus cognitive behavioral versus humanistic versus psychodynamic, and so on.
Also, it sounds like your client is might be asking for skills training. That learning breathing techniques are great, but they'd like more to take with them out into their lives. I'm a fan of ACT and EET for experiential exercises to teach skills, but you do you. You can lean on your theoretical orientation to find what processes to target and what skills to teach, given that client's particular needs.
actually, I've found an "old" comment of mine with the stuffs that may help you with your anxiety (at least for now):
https://www.reddit.com/r/exchristian/comments/phs1i8/comment/hbl7u0c/
it contains a link for steven universe video about meditation/dealing with anxious thought and another video to vatar (aang) about how to clean the chackras.
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although they sound sort of new-age stuff, they are well ilustrated and at least will offer you another lens of view.
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something that may take time is reading ACT Made Simple .
although it is a book written for therapists, you can find some help within.
of course, the default advice is to find a therapist that will help you navigate through such feelings.
But that's not always possible or at hand, so books about ACT (like the above) DBT and a few other theurapetical practices may work as a clutch for now.
but that's no excuse to avoid proper medical care. do therapy as soon as possible.