"Nodded off" is a phrasal verb meaning to fall asleep, and the antonyms for this expression can be verbs that denote staying awake or remaining alert. Words that are opposite in meaning to nodded off include staying awake, being vigilant, remaining attentive, and staying conscious. Other antonyms for this verb may include words like alert, active, vigilant, awake, conscious, watchful, and attentive. Additionally, words like energized, stimulated, lively, and animated can also be considered antonyms for nodded off as they denote energy and alertness, whereas "nodding off" denotes a state of sleepiness or drowsiness.