Sleeping humpback whale captured in rare footage

This fascinating footage shows a humpback whale taking a nap underwater.

The huge creature can be seen hanging upside down in the sea, one fin outstretched, its tail just floating on the surface.

Underwater research and video production team Panga MX encountered the sleeping humpback whale during a research project earilier this year.

Team member Kieran Bown posted the clip on YouTube, writing: "During a research project throughout January to April 2014 we encountered a sleeping Humpback Whale and managed to get an in water encounter with her. This is a short clip of a 20 minute encounter showing her come up to breath and check us out."

Unlike human beings, humpback whales are conscious breathers, which means they have to remember to breathe, even while sleeping, reports the Huffingotn Post.

Although they are not able to breathe underwater, whales are able to conserve energy and make one breath last for up to an hour.

According to Animal Planet, it's believed that humpback whales only shut off half of their brain at a time while asleep, so as to be alert enough to breathe.

This means they can float near the surface, replenishing their oxygen supply when necessary and remaining alert to potential threats, reports News.com.