The predominant symptoms of stomach flu are vomiting and watery diarrhea. In most of the cases, this illness also leads to infections in the upper region of the small bowel. In a few cases, this condition becomes the sole cause of the inflammatory infections observed in the colon. The affected person experiences unusual pains at the lower region of the abdominal which does not reach acute levels in most of the infected people. People experience immense loss of appetite which leads to fatigue, weakness and nausea in few. Abdominal cramps, headaches and high fever are yet other common symptoms of this illness.  

In rare cases, people also witness the passage of blood rich urines as one of the symptoms of this condition. Also, blood stained diarrhea is a symptom of severity of this illness which indicates a heavy concentration of bacterial colitis in the body. In children, gastroenteritis may make the child lethargic, weak and dehydrated. He may sometimes vomit bile, regardless of the empty stomach. Adults and children may experience the development of sunken eyeballs, dark colored eye circles and discoloration in the skin color. This condition may become a major cause of sleeplessness at night among children and adults.