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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Dieters who sleep more take off more fat that those who sleep less.
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Bats sleep 18-20 hours per day.
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Cows can sleep standing up, but they can only dream lying down.
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The average cat sleeps about 2/3 of the day.
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The record for the longest scientifically documented period without sleep is 264.4 hours (eleven days).
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