> One day, I didn’t feel anxious at all but I noticed that I couldn’t take a full deep breath most of the time.
What you experienced is called hyperventilation. It's when you breathe so much that you have exhaled too much CO2, causing a pH change in your blood. You then responded with fear that led to recurring panic attack (panic disorder).
I am surprised you didn't use the term 'hyperventilation'. Several years ago I had a similar episode, developing chest pain and recurring panic attacks (panic disorder) due to hyperventilation. In the past I also had moderate (to severe) anxiety.
It was debilitating, but I've resolved my issues with techniques learned through therapy. You might be interested in reading: https://news.ycombinator.com/item?id=23279349