I was just telling my therapist the other day that I feel so uncomfortable in my own body now because I don't trust it. Because it's always doing weird things. Breathing is one of them. I always feel short of breathe, or like my lungs won't expand all the way but My oxygen shows as normal. I also went to see a pulmonary Dr and they did tests and said my lungs are healthy and strong. Idk why I always feel like this but I hate it. My suggestion to you is to buy an oxygen monitor and use it when you feel this way as a reminder that you're lungs are fine. Also make an appt with the pulmonary dr and run tests just to be sure

Do some calming excerises and breath and if it doesn't go away then you'll know