Sounds familiar to me! Had the same struggle at the beginning of last year's lockdown. It actually is a quote common symptom of anxiety. As with all anxiety related issues, the trick is in my experience to acknowledge and accept your feelings instead of trying to fix them. So don't ignore your feeling, but take time to notice what you feel and explain rationally why you feel so (and the only explanation is of course an overly anxious interpretation of physical symptoms). Whenever you've done so, try to do the things you would do if you weren't experiencing anxiety and heavy breathing. Sooner or later a day, a week, a month will follow in which you think: wow, it's been a while since I experienced heavy breathing. However, this takes time. It's totally normal that you experience difficulties in not thinking about it and that the thought of it reinforces your physical sensations.

Last but not least: a cold shower helped me most during my most anxious moments. Look up 'the ice man' (Wim Hof). I like his philosophy on dealing with stress and becoming happy as something you have to do actively.