Dear client
Overthinking can be aspect of your personality. It could be anxiety . It could be reaction to real or imagined situation. It could be obsession like thinking about recent crush🙄.So it could be anything. But chronic fatigue syndrome is a definite disorder with its set of symptoms.
Next Steps
you can stary with learning relaxation and breathing exercises. You can distract yourself through hobbies, friends etc.
Health Tips
You can seek help of a psychiatrist or counselor. Some antianxiety medicine will be helpful.