Another cause might be hysteresis effect of insulin action, i.e., the effect of insulin is still prominent even if both plasma glucose and insulin levels were already low, causing a plasma glucose level eventually much lower than the baseline level.Sugar crashes are not to be confused with the after-effects of consuming large amounts of protein, which produces fatigue akin to a sugar crash, but are instead the result of the body prioritising the digestion of ingested food.The prevalence of this condition is difficult to ascertain because a number of stricter or looser definitions have been used. It is recommended that the term reactive hypoglycemia be reserved for the pattern of postprandial hypoglycemia which meets the Whipple criteria (symptoms correspond to measurably low glucose and are relieved by raising the glucose), and that the term idiopathic postprandial syndrome be used for similar patterns of symptoms where abnormally low glucose levels at the time of symptoms cannot be documented. To assist in diagnosis, a doctor may order an HbA1c test, which measures the blood sugar average over the two or three months before the test. The more specific 6-hour glucose tolerance test can be used to chart changes in the patients blood sugar levels before ingestion of a special glucose drink and at regular intervals during the six hours following to see if an unusual rise or drop in blood glucose levels occurs.
Suggestions include sugary foods that are quickly digested, such as:

Dried fruit
Soft drinks
Juice
Sugar as sweets, tablets or cubes.The anti-hypertensive class of medication known as calcium channel blockers could be useful for reactive hypoglycemia as inhibition of the calcium channels on beta islet cells can help prevent an overproduction of insulin after a meal is eaten. Postprandial syndrome
If there is no hypoglycemia at the time of the symptoms, this condition is called idiopathic postprandial syndrome. It might be an "adrenergic postprandial syndrome" — blood glucose levels are normal, but the symptoms are caused through autonomic adrenergic counterregulation. Often, this syndrome is associated with emotional distress and anxious behaviour of the patient. This is often seen in dysautonomic disorders as well. Dietary recommendations for reactive hypoglycemia can help to relieve symptoms of postprandial syndrome. See also
Spontaneous hypoglycemia
Refeeding syndrome

References
Further reading
Açbay O, Celik AF, Kadioğlu P, Göksel S, Gündoğdu S (1999). "Helicobacter pylori-induced gastritis may contribute to occurrence of postprandial symptomatic hypoglycemia". Dig. Dis. Sci. 44 (9): 1837–42. doi:10.1023/A:1018842606388. PMID 10505722. External links

Article about hypoglycemia at eMedicine