The phrase "caught some zs" is a colloquialism that is used to describe a person or an animal sleeping or taking a nap. The exact origin of the phrase is somewhat unclear, but it has become a popular expression in modern times. If you were looking for antonyms for this phrase, you could look at words that describe an active or alert state, such as awake, vigilant, alert, or active. In contrast to the phrase "caught some zs," using these words would imply that a person is fully awake, alert, and engaged in their surroundings, rather than asleep or taking a break.