People who suffer from gastroenteritis can notice lethargy among the symptoms. It is a full absence of energy, which makes the person rather drowsy. Of course, various stressful situations and overwork cause lethargy. Another reason is the lack of physical activity. To get rid of gastroenteritis, the organism invests all of its resources in the battle with the virus. It is not normal for such condition to last for more than 48 hours – contact your doctor then.