i used to get that. felt as if the diaphragm was not working properly. only happens nowadays if i get slack with the magnesium intake - it's important for muscle function. shortness of breath is no fun that's for sure! in my case the ms connection was taking lots of vitamin d3 to help my ms, but i did not balance my mineral intake properly. once i upped the mag it was much better. none of this may apply in your case, but there it is
might be helpful. take care!