The phrase "dead on one's feet" typically refers to a person who is extremely tired or exhausted. There are several antonyms for this phrase, including energized, refreshed, rejuvenated, and invigorated. These words convey a sense of renewed energy and vitality, indicating that the person is no longer tired or worn out. Other antonyms might include alert, awake, and lively, all of which suggest a person who is fully awake and engaged with the world around them. By using antonyms for "dead on one's feet," it is possible to convey a wide range of emotions and moods, from exhaustion to energy and from lethargy to enthusiasm.