CFS, or chronic fatigue syndrome, is a disease characterized by unusual tiredness that gets worse with activity but does not improve with rest. also called myalgic encephalomyelitis (ME), CFS is often diagnosed when an individual feels extremely fatigued for over 6 months. other symptoms include sleep that isn't refreshing, difficulty with memory/focus/concentration, and dizziness which gets worse when moving from lying down or sitting to standing. CFS has no known cause, but genetic predisposition is suspected. some things that can trigger CFS to develop are viral infections, immune system problems, hormonal imbalances, and physical or emotional trauma.