Chronic fatigue syndrome (CFS) is a long-term illness with a wide range of symptoms. The most common symptom is extreme tiredness.

CFS is also known as ME, which stands for myalgic encephalomyelitis. There’s some debate over the correct term to use for the condition, but these pages will refer to it as CFS/ME.

CFS/ME can affect anyone, including children. It’s more common in women, and tends to develop between your mid-20s and mid-40s.

It’s not known what causes CFS/ME, but there are a number of theories – for example, it may be triggered by an infection, or certain factors could make you more likely to develop the illness.