Fatigue of fatty liver disease is not common fatigue. It is a constant feeling of low energy, even after adequate rest. The liver plays a key role in converting nutrients into energy. When fat is built up in it, this energy process slows down. Over time, you can feel drained, heavy or sluggish, especially during the day. It is often dismissed as stress or overwork, but when fatigue becomes a daily companion, it may be worth paying closer attention.