Fatigue: One survey found that 76% of people treated for various forms of cancer frequently felt fatigued -- for some the kind of persistent exhaustion and weakness that makes it hard to do everyday activities.

Making matters worse, chemotherapy can decrease red blood cell counts, causing anemia, which in turn causes fatigue.

While drugs can stimulate the production of red blood cells, the problem may be more complex, says James Rigas, MD, director of the Comprehensive Thoracic Oncology Program at the Norris Cotton Cancer Center in Lebanon, N.H.

For some patients, "it's not just anemia. Correcting their anemia is not making their fatigue go away," he tells WebMD.

No matter what the cause, you don't have to let fatigue get the best of you. To cope, try attending to the highest priorities in your life first. Don't waste energy on unimportant things -- and be sure to accept help from family, friends, and neighbors.

And get plenty of rest during your treatment, though being too inactive can make things worse, says the American Cancer Society. An exercise program can help some, but check with your doctor to see if that's right for you.