What could have caused my mother's loud breathing?

This morning when my mother was walking across the living room floor I could hear her breathe. It was very loud. It sounded like it was coming from a big empty space in her chest. The only other time I had heard such loud breathing was from someone who had serious strokes in the past that affected his breathing.

My mother and I made it through church fine, though she was more confused than normal. We went out to lunch with no problem.

But still I wonder what could have caused the loud breathing. It was dry and not rattling. It was through her nose and she looked normal. But I could hear it from several feet away. Any ideas what causes this?