My Husband Is Feeling Dizzy. He Fell And Blacked Out

My husband is feeling dizzy. He fell and blacked out a few minutes ago. I was able to finally get him back in bed, but he says he feels like he is drunk ( he is not). He has had an upper respiratory infection for about a week now and has been taking Musinex dm. Do you think that his dizziness is related to the upper respiratory infection or could it be something neurological? When I say blacked out, I mean his eyes were open but he was not responding to his name for several minutes. He did not hit his head.