When sleeping, dolphins often rest motionless at the surface of the water, breathing regularly or they may swim very slowly and steadily, close to the surface. In shallow water, dolphins sometimes sleep on the seabed rising regularly to the surface to breath.

Dolphins do not "sleep" in the same way humans do; instead, they engage in unihemispheric slow-wave sleep. This means only half of their brain shuts down at a time, while the other half remains awake to control breathing and monitor for predators like sharks. Because they are conscious breathers, they cannot fall into a deep, unconscious sleep or they would drown. At night, dolphins generally stay in the same general area where they spend their day, but their behavior shifts to a state of "logging." During this time, they float near the surface, relatively motionless, or swim very slowly in a rhythmic pattern. Some coastal species may move into shallower, more sheltered waters at night to avoid offshore predators, while others may stay in deeper channels. In 2026, researchers using specialized night-vision and acoustic monitoring have found that some pods actually become more "vocal" at night, using echolocation to maintain contact while in their resting state, ensuring that the group stays together even when half the brain is "offline."