Anergy, meaning the lack of energy or immunological response, can have a variety of antonyms depending on the context. In terms of energy, antonyms could include vitality, vigor, stamina, or strength. When referring to an immunological response, antonyms may include response, alertness, reactivity, or sensitivity. It is important to note that the antonyms of anergy may not always be direct opposites, as they can depend on the specific use of the word. For example, in a medical context, the antonym of anergy may be hypersensitivity, whereas in a general sense, it could be efficiency or effectiveness.