Eerie video of Sperm Whales sleeping vertically 

The scene is both eery and beautiful when these sperm whales flip upside down – as if ready to begin a dive – and take catnaps with their pods. Hanging motionless in the water for up to 12 minutes (a brief time compared to their one-breath-dives that can last up to 90 minutes), these gentle giants are able to nap with half of their brains off, an act that is common among cetaceans. By shutting off only half of the brain, whales ensure that they are focused on both resting AND breathing.

Unlike respiratory systems in humans, the respiratory system of a dolphin or whale is voluntary meaning cetaceans must keep at least part of their brains awake in order to “trigger” each breath. They hang vertically at the waters surface so that they have quick and easy access to oxygen when needed.

Whales spend about 7.1 percent of their time asleep, and on a super interesting note, scientists have discovered that whales even exhibit signs of REM sleep (or the phase of sleep in humans that coordinates with dreaming)!

From:
DiscCh. - The Magic of the Big Blue 4of7 Europe - Sperm Whales Sleeping