Without sleep, our bodies have trouble regulating their temperatures, which means that as we feel fatigued, our brains may become hotter. Even if you have a cool room, this can lead to heatstroke. Getting less than six hours of sleep per night can lead to feeling hot even when it's cold outside. Your body is not using the energy it needs from sleeping so it turns on the heating mechanism to keep itself warm. This can lead to insomnia due to the body's attempt to stay warm overnight. Sleep helps your body produce anti-inflammatory chemicals and rid itself of waste products. So by staying up late without sleeping, you are doing your body more harm than good. Being tired can also make you feel hot because when you are sleepy, you use more of your energy state called "thermal energy". Thermal energy is the ability of any substance, including humans, to change its temperature. As you sleep more, you use more thermal energy, which makes you feel hotter. Finally, being tired can make you feel hot because when you are sleepy, your blood flows more slowly to your skin, leaving it vulnerable to heat exposure.