Nodding off is a phrase that describes the action of falling asleep or dozing off, and some antonyms may include words like waking up, staying awake, alert, wide awake or attentive. These antonyms convey the opposite of the reflexive movement from the head down to the chest, which is typically associated with nodding off, as these words suggest states of increased awareness and attentiveness. Alternatively, synonyms for nodding off may include words such as drifting off, drowsing, or slumber, which convey similar states of loss of consciousness or fatigue. Choosing the appropriate antonyms for nodding off will depend on the context of usage and the desired meaning of the author or speaker.