The keto flu can bring several unpleasant side effects, such as nausea, vomiting, headaches, and tiredness. These symptoms appear as the body adjusts to operating with a lower amount of carbohydrates and moves into a state of ketosis, which is the metabolic condition resulting from eating fewer carbohydrates. Transitory imbalances bring on symptoms in the body's mineral levels, insulin levels, and energy sources. These imbalances can also bring on symptoms.