The patient may complain of feeling exhausted and extra tired all day long. It happens as the organism lacks energy as a digestive system misbehaves, preventing the necessary nutrients form staying in the human body. No matter how much a patient rests, he is still sleepy. Sure thing, many health conditions are predetermined by ongoing fatigue, but you probably have gastroenteritis if this symptom is supported by diarrhea and some other signs. It is not normal if a fatigue lasts for more than 48 hours.