Some people have a "natural alarm clock" allowing them to wake up when they want. This is actually caused by a burst of the stress hormone adrenocorticotropin.
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Quick naps not only improve your alertness, but they also help in decision making, creativity and sensory perception.
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One reason that kittens sleep so much is because a growth hormone is released only during sleep.
212
The average person falls asleep in seven minutes.
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Bats sleep 18-20 hours per day.
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47% of people have a nightmare at least once a month.
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A hippo sleeping underwater automatically rises to the surface every ~4 minutes and breathes without waking.
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