Circadian rhythm

The main reason why feeling sleepy can affect how warm or cold we feel has a lot to do with our circadian rhythm – aka our body’s internal clock. As you probably already know, the circadian rhythm is responsible for a whole host of bodily functions, including the all-important sleep-wake cycle.

“The circadian rhythm is generated in a region of our brains called the hypothalamus and is affected by external cues such as the light-dark cycle of the sun, exercise and temperature,” Briscoe says.

Your circadian rhythm also has the power to influence your internal temperature – and it’s this ability which leads us to feel cold or shivery when we’re sleepy or tired.

Why? It’s all to do with the way our body temperature fluctuates to prepare for sleep. “Our core body temperature is approximately 37°C but fluctuates by about two degrees throughout the course of the day,” Briscoe explains. “A drop in core body temperature is a signal for our bodies to prepare for sleep and body temperature starts to fall about two hours before habitual sleep time.”

This is why you get all cold and shivery when you’re tired