Why test for fatigue?
Fatigue that doesn't improve with rest is one of the most common reasons people see a doctor, and a handful of blood tests explain most cases. Iron-deficiency anaemia, an underactive thyroid, and low vitamin D or B12 are frequent, very treatable causes in India.
A sensible first step is a Complete Blood Count with iron studies, a thyroid test, and vitamin D and B12 — plus a blood sugar check if you have risk factors for diabetes. Your doctor interprets these together with your symptoms.