| The fatigue must be: | Clinically evaluated |
| Unexplained |
| Persistent or relapsing |
| New or definite onset (not lifelong) |
| Not the result of ongoing exertion |
| Not substantially relieved by rests |
| Results in substantial reduction in previous levels of occupational, educational, social or personal activities |
| Four or more of the following symptoms: | Substantial impairment in short-term memory or concentration |
| Sore throat |
| Tender cervical or axillary lymph nodes |
| Muscle pain |
| Multiple joint pain without joint swelling or redness |
| Headaches of a new type, pattern or severity |
| Unrefreshing sleep |
| Post-exertional malaise lasting more than 24 hours |