Severe cough. Chest x ray normal!

Since like last2-3 years my father is having night time cough, he complains dryness and that may be he unconsciously he start breathing from mouth while sleeping, but i think otherwise, he is just ignoring it and not consulting a specialist, may be he is right. But what happens is this cough is not regular but it happens every once in a while sometimes 3 times in a week sometimes 3 times in 3 month, and its not the onl y issue in these last three years he had kind of severe cough attack, if this word makes aense, he has a habit of clearing his throat quite heavily and sometimes (4 times in last 2 year) he when start to clear his throat, he starts to cough and cough more heavily , so much severe cough that he cant even breath and can not able to stop himself and i feel helpless at that moment what should i do, these cough attack stay for like 3-5 minutes but the intensity is so much that he cant even breathe, even the night time cough sometime has this intensity..chest x ray normal