Understand why you really need

Nighttime Body Temperature

Human bodies are wired to cool off during the nights. So, just before we are about to sleep, we need a cooler temperature to ensure a good night's sleep. As we fall asleep, our body also tends to lose heat; that's why we start feeling cold 2-3 hours after falling asleep. Although while you're sleeping, it can be 1 to 2 degrees lower than in the daytime. This continues until an hour or two before we wake up.
 

Ideal Room Temperature

Normal human body temperature is between 36-37 degree Celsius, so the ideal room temperature should be around 24-28 degree Celsius with sufficient airflow. Unfortunately, people tend to set their AC at 18-21 degree Celsius, believing it will be more comfortable for them. However, running AC at a low temperature throughout the night can lead to low humidity. This can dry out your sinuses, increasing the risk of respiratory infections.