When one is fatigued, he or she feels tired, exhausted, languid, or listless. An individual can be physically fatigued, mentally fatigued, or both. Physical fatigue is essentially the tiring of muscles. When muscles tire, they become unable to perform optimally. Excessive physical activity in relation to a person’s fitness level can cause physical fatigue as can a lack of rest as well as stress and anxiety. Mental fatigue, on the other hand, occurs when one cannot perform optimal cognitive activities or functions. In essence, mental fatigue is a decreased level of consciousness, which can occur from stress, anxiety, lack of rest, and emotional duress. Ultimately, though, fatigue can occur due to a wide range of conditions, diseases, injuries, and ailments as can malaise, which is a feeling of being uncomfortable, unwell, out of sorts, or uneasy. When one experiences malaise, he or she may describe it as a warning-like sensation that something isn’t right. Often, both malaise and fatigue are the first indicators of infection, illness, or disease. Treatment for fatigue when not associated with a more serious condition is rest whereas the only way to address malaise is to see a medical professional, who through an initial examination and possibly diagnostic tests can determine its cause.