A hippo sleeping underwater automatically rises to the surface every ~4 minutes and breathes without waking.
23
The harder you concentrate on falling asleep, the less likely you are to fall asleep.
34
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.
15
Sea otters hold hands while sleeping so they don’t drift away from each other.
104
In China, teachers allow children to sleep in class for around 20 minutes to help improve their learning.
13
Lack of water is the #1 trigger of daytime fatigue.
148
The higher someone’s I.Q. the more likely they are to be sleep deprived.
29