We all experience daytime fatigue. To some, fatigue means trying to stay awake during that last hour of work after the caffeine crash hits. To others, fatigue is an ongoing symptom of underlying illness or disorder. No matter the cause or severity, fatigue is a potentially debilitating phenomenon that affects how we work, think, and process. Fatigue can cause issues such as poor memory, depressed mood, and irritability. Long-term, it can also cripple your social life and lead you to turn down opportunities that you just don’t have the energy to pursue.