Medically speaking, tiredness happens to everyone -- it’s an expected feeling after certain activities or at the end of the day. Usually, you know why you’re tired, and a good night's sleep solves the problem.
Fatigue is a daily lack of energy; unusual or excessive whole-body tiredness not relieved by sleep. It can be acute (lasting a month or less) or chronic (lasting from 1 to 6 months or longer). Fatigue can prevent a person from functioning normally and affects a person's quality of life.