chronic fatigue syndrome

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A syndrome characterized by debilitating fatigue and a combination of flulike symptoms such as sore throat, swollen lymph glands, low-grade fever, headaches, and muscle pain or weakness.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun pathology A condition characterized by immune, endocrine and neurologic pathology whose main symptoms are extreme fatigue, extremely low stamina, muscle pain, lymph node swelling, post-exertional Malaise, and cognitive difficulties.