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Chronic fatigue is a complex medical condition characterized by extreme and persistent fatigue that is not relieved by rest and is not directly caused by other medical conditions. The key aspects of chronic fatigue include:
- Long-term fatigue lasting at least 6 months that significantly interferes with daily activities and work/school life
- Post-exertional malaise (PEM) - increased symptoms and worsening fatigue after physical, cognitive, or emotional exertion
- Sleep dysfunction - unrefreshing sleep or altered sleep quality
- Cognitive impairment - problems with short-term memory, concentration, processing speed
- Flu-like symptoms - sore throat, tender lymph nodes, muscle and joint pain
The exact cause of chronic fatigue is unknown but may involve:
- Infections - Exposure to certain viral infections may be a trigger
- Immune dysfunction - Increased inflammatory cytokines and impaired natural killer cell function
- Mitochondrial issues - Problems with cellular energy production
- Brain and nervous system - Changes in neuroendocrine signaling, HPA axis dysfunction
There are a few names used interchangeably for chronic fatigue:
- Myalgic encephalomyelitis (ME) - Post-infectious disease characterized by inflammation of brain and spinal cord
- Chronic fatigue syndrome (CFS) - General term for unexplained, long-term fatigue not relieved by rest
- Systemic exertion intolerance disease (SEID) - Emphasizes the post-exertional worsening of symptoms
This answer defines chronic fatigue, outlines the key symptoms, and covers some of the hypothesized disease mechanisms and terminology.