The phrase "happy go lucky" refers to someone who is carefree and lighthearted. Antonyms for this expression might include words like anxious, troubled, or solemn. A person who is "anxious" might experience constant worry and fearful thoughts about the future, while someone who is "troubled" might be weighed down by problems or difficulties. "Solemn," on the other hand, suggests a lack of joy or levity, often associated with formal or serious occasions. While antonyms for "happy go lucky" may vary depending on the context, they generally imply a sense of concern, seriousness, or sadness.