This document discusses the concepts of physical and mental fatigue. It defines fatigue as a subjective feeling of tiredness that is distinct from weakness and can be alleviated by rest. Physical fatigue is the temporary inability of muscles to perform optimally due to factors like exercise, while mental fatigue is a temporary decrease in cognitive performance from prolonged cognitive activity. Both types of fatigue can be caused by lack of sleep, stress, overexertion and other factors. The document also discusses emotional exhaustion and provides classifications of different emotions.