EzineArticles.com: Fatigue is described as the loss of strength due to low energy levels during or after a strenuous mental or physical activity. You experience fatigue because whatever activity you were doing has drained you of energy which you did not replenish or take a rest from. Physical fatigue is experienced when you find you have less energy to do the physical activities you usually find easy to do.

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What Can Cause Fatigue and Rapid Weight Loss?