Sharks do not sleep like humans or other animals do.
However sharks do need to rest and they do stop some and rest in parts of the water.
It may seem like the shark is actually sleeping but the shark is just not moving and is resting.
After the shark gets done resting and is fully rested up and has more energy then the shark starts moving again.
Some sharks do need to swim constantly but some sharks do rest and some sharks such as the nurse shark have spiracles that force water across their gills allowing for stationary rest.
So some sharks do swim all the time and hardly if ever rest while some sharks do need rest and do rest but the sharks do not really sleep at all like we do.