In general, in order to receive a diagnosis of Chronic Fatigue Syndrome, a patient must satisfy two criteria:

Have severe chronic fatigue of six months or longer duration with other known medical conditions excluded by clinical diagnosis, and
Concurrently have four or more of the following symptoms:

• Substantial impairment in short-term memory or concentration.
• Sore throat.
• Tender lymph nodes, muscle pain.
• Multi-joint pain without swelling or redness.
• Headaches of a new type, pattern or severity.
• Unrefreshing sleep.
• Post-exertional malaise lasting more than 24 hours.

Source: Center for Disease Control
To learn more about Chronic Fatigue Syndrome, click here.