When it comes to describing sleep, "catches some z" is an informal and playful way to express the act of sleeping. However, when it comes to finding antonyms for this phrase, we can look towards its more formal counterparts - such as "resuming wakefulness" or "awakening". Other potential antonyms could include "staying awake", "staving off tiredness", and "fending off exhaustion". Whatever the opposite of "catching some z" may be, it's clear that there are plenty of ways to describe remaining alert and awake - even if "catching some z" remains the cozier option.