Food allergy particularly can cause this fatigue and is often unsuspected and undiagnosed, especially because one or two or three days could pass after the ingestion of the food before the symptoms occur so they would not necessarily be suspected as due to the ingestion of the food. Some patients report overwhelming fatigue and sleepiness, occasionally within hours of eating a certain meal, and they can only resort to lying down and taking a twenty or thirty minute nap since nothing else seems to help. Some patients have actually used antihistamines with moderate success. When fatigue follows eating, and is relieved by a short nap, one needs to be suspicious of allergy. This is not due necessarily to pooling of blood in the so-called splanchnic areas, i.e. in the gut, but can be truly an allergic reaction which in part is central in origin, i.e. the nervous system is affected.