Same issue here. Never had a sleep issue in the past, suddenly waking up short of breath every night around 2-3am. On a bad night it can repeat 5-10 times. Makes life very difficult. I share your frustration with the default answer to any unanswered medical condition being stress or anxiety.
If you mention waking up at that time many go straight to stress as cortisol levels increase around that time. They increase at this time for everyone - not just those waking up at 2am.

I am still working on solving my issue but i believe it is related to my stomach. After waking i often burp. I think bloating puts pressure on my diaphragm making breathing more difficult, and i think this might be waking me. Trying Antacids, De-gas medication - not having much luck. Also altering my diet and excluding things that can cause bloating like lactose. I have stopped eating late which definitely helps. I am booked in to see a Gastro and hopefully he will provide some feedback.