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Your body follows a natural 24-hour rhythm called the circadian rhythm. This internal clock helps control when you feel sleepy, hungry, energetic, or alert. It also influences body temperature, hormone production, and digestion. Sunlight is one of the biggest factors that keeps this clock on schedule.
Disrupting it with irregular sleep can affect both your mood and health. Your body always knows roughly what time it is—even without looking at a clock.
© National Institute of General Medical Sciences