catching some ZZZs

Catching some ZZZs is a cliche which is referring to the act of sleep. Someone who is going to catch some ZZZs is talking about going to sleep or taking a nap. The idiom of catching some ZZZs comes from comic strips and cartoons in which ZZZ is the symbol of the cartoon character being asleep and dreaming. Therefore, catching some ZZZs, means to fall asleep as well as dream in many cases.