The phrase "mellow out" generally refers to becoming calm, relaxed, or less agitated. Antonyms for "mellow out" include phrases like "get worked up," "become aggressive," "panic," "stress out," "freak out," or "lose your cool." These antonyms indicate a state of heightened emotion or anxiety, as opposed to the relaxed state associated with "mellowing out." Someone who is unable to "mellow out" may experience a range of negative feelings, such as anger, frustration, or anxiety. Understanding antonyms can help us to better understand the nuances of language and express ourselves more accurately in different situations.