Some people find pneumonia cough especially worse at night. Some possible reasons for pneumonia cough worsening at night are:
Ineffective phlegm removal: During the day, you are more active. You may have been coughing at regular intervals, keeping your airways clean. At night, phlegm may accumulate, potentially waking you up with forceful coughs.
Post-nasal drip: Some people get more mucus in the back of the nose and throat when they have pneumonia. During the day, mucus stays down due to gravity and you clearing your throat from time to time. At night, mucus may accumulate in the back of your throat, making you cough.
Acid reflux: Stomach acid usually increases during sickness and stress. When you lie down at night, stomach acid may flow backwards to your throat, making you cough.
There are no clear-cut ways to help reduce pneumonia cough at night. Sometimes, keeping your head higher with a propped pillow may help. If you have increased mucus, an antihistamine such as Benadryl may help. If you have other symptoms of acid reflux, you can try an OTC acid reducer. Call your doctor if your symptoms worsen.