Dolphins do not breathe automatically, breathing is always done on a conscious level. As mammals, they nevertheless need regular sleep, i.e. a state without consciousness, so that their bodies remain functional. How can dolphins sleep without suffocating?

Dolphins can never be completely unconscious in order to continue breathing. They must therefore remain at a certain conscious level even when sleeping. They do this by alternately putting the brain hemispheres into an unconscious state. One hemisphere "sleeps" while the other controls breathing. This gives the respective hemisphere of the brain the recovery phase it needs to regenerate. The dolphins' sleep phase, i.e. the alternating resting of the brain hemispheres, lasts around eight hours per day.