Sleepyheaded is an adjective used to describe someone who is feeling drowsy or lacking energy. Some antonyms for this word include alert, awake, energized, lively, and wide-awake. Alert means being watchful, attentive, and aware of one's surroundings. Awake means being conscious and aware of what is happening. Energized means having a burst of energy or feeling revitalized. Lively refers to being full of energy, animated, and enthusiastic. Wide-awake is similar to awake, but it emphasizes being fully aware and alert. Overall, these antonyms convey the opposite of sleepyheadedness and provide a sense of energy, enthusiasm, and awareness.