The human brain is more active during sleep than during the day.
28
Lack of water is the #1 trigger of daytime fatigue.
148
Cows can sleep standing up, but they can only dream lying down.
745
Sleeping on the job is acceptable in Japan. It is viewed as exhaustion from working hard. Some people fake it to look committed to their job.
57
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
A hippo sleeping underwater automatically rises to the surface every ~4 minutes and breathes without waking.
23