For some people, tiredness does not disappear after breakfast, coffee or even a full night's sleep. They wake up feeling unrefreshed, struggle to concentrate during the morning, experience an afternoon slump and reach the evening feeling as though the entire day has required more energy than they had available. Psychology and sleep science suggest that daytime fatigue is not simply a question of how many hours someone slept. Sleep pressure, circadian rhythms, mental fatigue, chronic stress and the quality of recovery can all influence how energetic a person feels. At the same time, persistent fatigue can have physical or psychological causes that should not be explained away as a personality trait.
