A dark night is good for your health
On its own, the circadian rhythm takes almost 24 hours. Our bodies rely on the Sun to reset this cycle and keep it at 24 hours, the length of our days. Light and the dark are important signals for the cycle.
During the night, body temperature drops, metabolism slows, and the hormone melatonin rises dramatically. When the Sun comes up in the morning, melatonin has already started falling, and you wake up.