WHY does the cough intensify at night?

 WHY does the cough intensify at night?

When a person remains in a horizontal position, mucus accumulates in the nasopharynx and the airways cannot be cleared. With a runny nose, secretions from the nose and sinuses drain into the throat and cause a cough reflex, so the coughing is worse when we sleep, especially when turning over from side to side, and in the morning when getting out of bed. Dust and dry air can make the cough worse. Dry and hot air irritates the mucous membranes and provokes coughing fits.