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
Staying awake for 17 hours is the same for your body as drinking 2 glasses of wine.
193
Blue light fends off drowsiness in the middle of the night, which could be useful to people who work at night.
240
In China, teachers allow children to sleep in class for around 20 minutes to help improve their learning.
13
The strangers in your dreams are actually people that you've seen in real life.
50
A hippo sleeping underwater automatically rises to the surface every ~4 minutes and breathes without waking.
23