What Causes Shortness Of Breath During Weight Training?

I have been experiencing mild shortness of breath and a feeling of not being able to take a good deep breath, this feeling gets worse when i weigh train, today, i felt as though i was going to pass out at the gym, so i left early and went home. I have been training for over ten years and have never felt like this, I am a 29 year old male, i believe i am in good shape, although have not had a full physical done on two years, on the last physical everything came back great, i was also hooked up on an ekg machine and everything came back great, again this was two years ago. I do have anxiety, and when my anxiety flares up it tends to be in the form of health anxiety, so maybe this is what this could be. Just me overthinking everything.