If there is a lack of glucose from not eating for example, the hormone glucagon is released from the pancreas which causes the liver to release glucose from storage so your body can function. Together, these hormones regulate glucose.
In diabetics, low glucose occurs when there is too much medication taken relative to the amount of glucose available. For example, taking insulin or other diabetes medications but forgetting to eat a meal will lead to low glucose levels.
Giving some form of sugar such as juice or candy is the treatment. Glucose levels should be monitored frequently after an episode of hypoglycemia to prevent re-occurrence.
In non-diabetics, the cause of hypoglycemia include hormonal deficiencies, tumors of the pancreas, excessive alcohol intake or critical illness. Urgent medical evaluation should take place to identify and treat the cause of low glucose.