too much coughing

My husband has had a cold for about 10 days now.  The past 3 days, he has been coughing alot, even with prescribed cough syrup.  Tonight he was coughing when I looked over and he was sitting limp and dispondent.  After about 30 seconds, he finally came around and says to me, "what are you looking at?  What happened?"  After discussing with him what I had just witnessed, he says that sometimes when he coughs so hard, he will pass out.  He felt a pain in his head just before he passed out and when he came to, his skin was gray, he was clammy, and his eyes were glazed.  After a few minutes, he was fine.  I am concerned about this and would like to know what happened to him.   Thanks.