"Sleep is a concept that we think about from a human standpoint," George Burgess, director of the Florida Program for Shark Research, told The Dodo. "There's no particular indication that sharks sleep like humans do, that is, they don't find a place to lay down, close their eyes and check out for periods of time. They reduce their activity level, but it doesn't mean they stop doing their normal activities"
Instead of sleeping the way we do, many types of sharks do something called yoyo swimming, according to Burgess When a shark is yoyo swimming, he stops actually swimming and just starts gliding downwards. He does this until he hits the ocean floor, and then he swims back up to the surface and does it again. By gliding down instead of actually swimming, the shark is able to take a period of rest, which is his version of sleeping.