Iam suffering from severe cough suddenly.when I was sleeping in night times the cough will come first the cough start lightly and then it go on increases and there will be severe cough.Again during morning there will be no cough.some times this type cough will come in day time also.it comes suddenly.after some time there will be no cough.it comes during night times daily and some times during day times.there will be no cold.i didn't have any smoking habits still iam getting severe cough.why it is coming???