Why does a 2-month-old baby sometimes cough while sleeping?

This may be due to the child’s frequent nasal discharge or nasal secretions; when lying flat at night, these secretions—or pharyngeal secretions—accumulate in the throat, causing airway obstruction and resulting in intermittent, paroxysmal coughing. In fact, this cough serves a protective function—to maintain unobstructed airflow in the respiratory tract. Postnasal drip (i.e., “leakage” of mucus from the back of the nose) is also a common cause of nighttime cough in children.