5. Fatigue Cause No. 6: Hypothyroidism
The thyroid is a small gland at the base of your neck. It controls your metabolism, the speed at which your body converts fuel into energy. When the gland is underactive and the metabolism functions too slowly, you may feel sluggish and put on weight.
6. Fatigue Cause No. 7: Caffeine Overload
Caffeine can improve alertness and concentration in moderate doses. But too much can increase heart rate, blood pressure, and jitteriness. And research indicates too much actually causes fatigue in some people.