Eupneic is a word that describes normal and easy breathing. Some opposite antonyms that come to mind are gasping, wheezing, and dyspneic, which describe breathing that is labored, wavering, and challenging, respectively. Similarly, breathless, asphyxiated, and suffocating are antonyms that indicate a lack or restriction of airflow. On the other hand, relaxed, calm, and peaceful are antonyms that describe breathing that is steady, effortless, and composed. Overall, antonyms can help us understand the opposite meanings of a word, in this case, a word that is related to breathing and respiration.