Losing energy is a common occurrence in everyday life. Fading, sagging, tiring, drooping, and flagging are all words that describe the process of losing energy. Fading is when something gradually becomes less visible or intense. Sagging is when something droops or hangs down due to a lack of support. Tiring is when something becomes weary or exhausted. Drooping is when something hangs down or bends due to a lack of strength. Lastly, flagging is when something loses its vigor or enthusiasm. All of these words describe the process of losing energy.