A sudden onset
Feeling like you are coming down with the flu, but it never goes away. There are cases where it develops more slowly but sudden onset is a big red flag. This is one of the big reasons why many believe there is a viral component to it.
Dull, aching pain in your muscles and joints
Dull, aching pain in muscles or joints that won’t go away and doesn’t respond to anything is another sign of chronic fatigue syndrome. It may develop into chronic headaches that are not migraines. The pain is often considered being in the fascia but moves around a lot and does not seem to be related to muscle use.