A research dive team called Panga MX caught some amazing footage in Mexico of a humpback whale slumbering straight up-and-down in the water, with its tail facing the surface.

In the video below, an abbreviated version of a 20-minute observation made by the team, the whale can be seen gently bobbing in the water. Eventually it drifts toward the surface in a horizontal position, floating on its back (or stomach, depending on which side a whale considers "up").

Whales have an interesting trick when sleeping -- they do it with half of their brain still open for business, as DNews reported in this 2011 video recounting a study of whale sleep that included captivating footage of a pod of sperm whales snoozing.

As the DNews video notes, whales nap in fairly brief intervals, because they need to surface for air. Land mammals such as humans breathe involuntarily, but undersea mammals such as whales and dolphins have to consciously choose to breathe. Sleeping with a shut-down brain, of course, would make that choice a difficult one to make. That's where the half-their-brain thing comes into play. A whale may be "sleeping" but it isn't so down for the count -- brain-function-wise -- that it won't be conscious of the need to come up for air.

One look at a humpback whale makes it easy to see why they need their rest. It must be tiring just being a humpback whale. They're enormous creatures that can grow to nearly 60 feet long and weigh a whopping 40 tons.