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Holly Phillips said. It's not clear why this happens ; studies suggest that in response to the stress of not getting quality snooze time, there's a reduction in activity in the hypothalamus, the control panel of the brain where body temperature is regulated. A study from the European Journal of Applied Physiology appears to back this up : researchers documented a drop in body temperature in 20 sleep-deprived young adults. Metabolism may be a culprit here as well. When you're fatigued from a restless night, your metabolism works at a more sluggish pace, Holly Phillips said, producing less heat and slower circulation. You're dehydrated Up to 60 percent of the adult human body is water, and water helps regulate body temperature.