What Causes Episodes Of Choking On Saliva?

My husband has had three episodes in the past month of "choking". He claims he is choking on his saliva. What I witness is extremely frightening...he stops breathing for anywhere up to 30 seconds, his face turns bright red, he shakes and gets a look of panic on his face as he fights to get his breath back again. He refuses to seek medical attention, not sure what else to do.