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
Bats sleep 18-20 hours per day.
5
You burn more calories sleeping than you do watching television.
348
Sea otters hold hands while sleeping so they don’t drift away from each other.
104
The human brain is more active during sleep than during the day.
28
There's a love mattress that is specifically designed for couples who sleep on each other's arms.
12
Cows can sleep standing up, but they can only dream lying down.
745