Low-energy can be described in various ways using synonyms. To start, one could say that a person is lethargic, sluggish or lacking in vigor. Alternatively, they may be described as apathetic or indifferent, showing no interest or enthusiasm in things. They might also be referred to as languid or listless, displaying little or no energy or movement. Other synonyms might include tired, weak or feeble, indicating a lack of physical strength or stamina. In terms of emotions, someone who is low-energy may be described as dispirited or dejected, low-spirited or downcast. Regardless of the exact word used, all of these synonyms reflect a state of being down, slow and not fully engaged.