It's difficult for me to reply because I don't know what to address - your stated question or the whole issue, and I'm not sure how to address the stated question in a way that will help you and not feed your anxiety (if indeed your allergies are entirely created by your anxiety).
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I've honestly never heard of a chicken or steak or blueberry allergy, though I admit I'm no expert. Dairy is a fairly common allergy and intolerance, though (doesn't mean you have it). I've heard of chocolate allergies but I don't think it's too common.
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As for whether it's possible for someone to suddenly develop an allergy after decades of eating a thing, it seems it is possible to develop an allergy or something like it. A damaged gut can have difficulty processing some things that were previously ok. Whether that can be classified as an actual "allergy" I'm not sure, but I'm assuming you're not fixated on pure allergies per se but whether someone can react to a food, or have difficulty processing it.
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Whether or not you are having true food issues or they are manufactured by your anxiety, I would encourage you to first and foremost try to address the anxiety. I speak from experience when I say that problems are extremely difficult to address while in the grip of anxiety. I don't know if you are receiving any help for it right now, but if you are not (and even if you are and it's not working) I'd focus on that as your number one priority. A lot of people, myself included, are reluctant to take medication, but I have come to believe that anxiety medication can be extremely useful as a first step.
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When you are feeling better in terms of your anxiety, you will be able to more accurately judge whether you are having true food issues that you need to explore. If you are, it won't feel so overwhelming to try to address them. Allergies and intolerances are not uncommon (though that doesn't mean you have any), and they are surmountable challenges. But if you are having such anxiety, I don't think anything I can say here will make you feel better about the food, and of course I would be entirely wrong to say that you do or do not have any allergies based on a post on the Internet.
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When I'm in the grip of anxiety, I feel overwhelmed, so I hope my reply will be able to help you focus on one action point, which might feel less overwhelming. While I'm sure your food anxiety is affecting your peace and maybe routines as well, the list of foods that you have deemed "ok" seems to have adequate variety and nutrition that it's not an emergency. If you had written that you can eat nothing but pears, that would be a different story.
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Also, sorry to hear about your mom. My mom had viral meningitis (the less severe kind) a couple months ago, and had to be hospitalized since she couldn't shake it on her own. She too seems to have some lingering illness now (in fact was rehospitalized this weekend). My mother's illness has definitely had an impact on my thoughts about my own health, though not anxiety or food issues. It's so scary to see the mortality of a parent, and additionally it implies our own mortalities.