I feel so much for you as you not only face the challenges that come with breathing through a mask but also the anxiety that comes from that in relation to your past experience.
While I only face the challenge of wearing a mask, without the anxiety, I'd come to question a lot about the masks. I work in aged care. At first it was just the mask, which was challenging enough, and then the face shields were added to that. The challenge with breathing while not feeling like you're suffocating, the challenge with the heat and the mental challenges that comes with those 2 factors combined was pretty mind altering to a degree. Working in the kitchen there meant that (we) the kitchen staff became exempt from wearing the shields. I feel deeply for everyone else who is left with the challenges of both the mask and the shield together. It really is horrible and quite suffocating when the harder you work/the faster you move, the more you feel the need to breath freely.
While a lot of the experts advise 'The masks don't change or impact your breathing' I beg to differ. Took me a while to discover I'd gone from being a nose breather to a mouth breather while I was wearing the mask. It was a completely different way of breathing for me, as I'd always been someone who breathed through my nose. My breathing also became more shallow. So, basically, I wasn't breathing 'properly' or easily. While those experts say the masks don't impact your oxygen levels, changing the way you breath behind a mask can. Mouth breathing vs nose breathing is some interesting research. I found it was handy to take a couple of toilet breaks outside of normal breaks. Just a minute or so for each one. It's a chance to take the mask away from your nose and mouth while you're sitting on the toilet. They're not really toilet breaks, they're breathing breaks. As long as this is managed carefully, such as with not sneezing or coughing and you're not picking up any sneezes or coughs someone else has left behind in the cubicle, it's a chance to literally take a breather.
I figure, considering we're not born with masks on our face, wearing a mask is simply not natural and we feel what's not natural. Not only is it not natural but you're doing what's not natural for an entire 3rd of the day (if you work an 8 hour shift). That's a long time to be doing what's far from natural. Btw, I found greater hydration makes a bit of a difference.
I hope you find what makes a big difference to you :)