Cough often gets worse at night because lying down allows mucus to drain into the throat and irritate the airways. During sleep, the airways can narrow slightly, and dry bedroom air may further aggravate the cough.

Since your cough is productive (with phlegm), Corex‑D is not advisable, as it suppresses the cough reflex and may prevent mucus from clearing, which can worsen your condition. A persistent nighttime cough with chest pain needs proper medical evaluation to rule out infection or other causes. It is strongly recommended not to take any medication on your own; treatment should only be started after a correct diagnosis and strictly under the supervision of a qualified doctor.