Antonyms for the word "mellowed out" includes words that are opposite in meaning such as agitated, anxious, hyper, manic, tense, or uptight. These antonyms suggest a state of being restless or worked up, rather than calm and relaxed. Some other antonyms related to "mellowed out" could be energized or invigorated, indicating a state of heightened activity or alertness. On the other hand, synonyms for "mellowed out" might include words such as relaxed, chilled, serene, or peaceful. These all bring to mind a sense of calmness and tranquility, rather than frenzied activity or anxiety.