Fatigue can come and go or stay constant for a while. Fatigue from chemotherapy tends to happen a few days after the treatment, peaks, and then gets better before the next treatment. Fatigue from radiation may not happen right away.
Fatigue is a vague feeling of being tired, weak, or exhausted. It is often a symptom of cancer when cancer is first diagnosed, or when cancer progresses. It is also the most common side effect of cancer treatment.