Why doesn't rest relieve cancer fatigue?

Cancer fatigue is different from the ordinary tiredness a healthy person feels. When a healthy person is tired, it is usually caused by activity and goes away after resting or sleeping.

Cancer fatigue is not completely relieved by sleep or rest, and it may happen after little or no activity. People often describe having no energy, feeling drained or heavy, having trouble thinking, and not feeling rested even after sleeping.

Because it works differently, cancer fatigue is managed in its own way. Tell your health care team if you feel very weak and tired—especially if you cannot do your normal activities or are still very tired after resting.