A pod of sperm whales sleeps in an upright position

So why might sperm whales choose to sleep vertically? There are several potential benefits to this position. For one, it allows the whales to conserve energy by remaining buoyant and not expending extra energy to stay afloat. It also allows them to remain vigilant, as they can quickly wake up and dive if danger approaches. Finally, sleeping vertically may allow the whales to socialize and maintain contact with other members of their pod.

National Geographic