Extreme fatigue that can't be explained by an underlying medical condition.

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is extreme fatigue that can't be explained by an underlying medical condition.

It may get worse with activity, but doesn't improve with rest. The cause is unknown.

Treatment focuses on symptom relief. Medicines for pain, depression and sleep can help. Other treatment options include counseling, physical therapy and working toward a good balance between activity and rest, known as pacing.