The phrase "caught some z's" is a colloquial term for getting some sleep or taking a nap. The antonyms for this phrase would be to stay awake, to be alert, or to be active. Other opposite phrases could include "pulling an all-nighter," "burning the midnight oil," or "staying up late." These phrases demonstrate the opposite action of sleeping or resting. While "caught some z's" implies a sense of relaxation and inactivity, its antonyms convey a sense of energy, productivity, and alertness. Therefore, it is important to understand the context in which these phrases are used to convey the appropriate meaning.