I felt oddly short of breath for a week or two recently, and it was persistent. It wasn't just a "I felt a little short of breath and it disappeared" thing, it was practically 24/7 for that week or two. Then I felt severely overwhelmed one evening while out with the family, had a moderate panic attack, and a few smaller attacks after that. And my breathing seems to have magically fixed itself. Could just be anxiety manifesting - which is common.
As for the stress test, I have always felt like I get out of breath easily. I can walk half a flight of stairs and feel like my chest is going to explode (bit of an exaggeration, but you get the idea). However, I had a stress test in 2016, and when they asked me to get off the treadmill I felt fantastic. Only when I sat down and relaxed did I notice the changes in breathing (caused by the exertion) and questioned if it was normal. Again, not unusual for anxiety.