Hypoglycemia (low blood sugar) happens when the amount of glucose in the blood drops below what the body and brain need for normal function, most often as a side effect of diabetes treatment but also from other medical and lifestyle causes. It can range from mild (hunger, shakiness) to severe and life‑threatening (seizures, unconsciousness) if not treated.

What hypoglycemia is

  • Hypoglycemia usually means a blood glucose level low enough to cause symptoms, often below about 70 mg/dL (3.9 mmol/L) in people with diabetes.
  • Glucose is the main fuel for the brain, so low levels trigger rapid hormonal and nervous system responses to restore sugar, which is why symptoms can feel sudden and intense.

Major causes in people with diabetes

  • Taking too much insulin or certain diabetes pills (especially sulfonylureas) is the most common cause of hypoglycemia in people with diabetes.
  • Skipping or delaying meals, eating fewer carbohydrates than usual, or vomiting while still having active diabetes medication in your system can drop your blood sugar.
  • Exercising more or longer than usual without adjusting food or medication, and drinking alcohol (especially on an empty stomach), also increase the risk.

Causes in people without diabetes

  • Serious illnesses like severe infection (sepsis), advanced liver disease, kidney failure, or heart failure can impair the body’s ability to maintain normal blood sugar.
  • Certain hormone deficiencies (such as adrenal insufficiency or lack of growth hormone) and rare tumors that produce insulin (insulinomas) or insulin‑like substances can cause recurrent hypoglycemia.
  • In newborns and young children, prolonged fasting, prematurity, inborn errors of metabolism, or maternal diabetes can trigger low blood sugar episodes.

Medication, alcohol, and lifestyle triggers

  • Beyond diabetes drugs, some other medications and drug interactions can lower blood sugar, especially when combined with poor intake or illness.
  • Alcohol suppresses the liver’s ability to release stored glucose, so heavy or binge drinking, particularly without food, is a well‑known trigger.
  • Factors like hot weather, changes in routine, puberty, or menstrual cycles can alter insulin needs and contribute to hypoglycemia in people using insulin.

Reactive and fasting hypoglycemia

  • “Reactive” hypoglycemia happens a few hours after eating when the body releases more insulin than needed for the meal, leading to a drop in blood sugar; this is sometimes seen after gastric surgery.
  • “Fasting” hypoglycemia occurs after long periods without food and is more likely to be linked to underlying conditions such as liver disease, hormone problems, or metabolic disorders.

TL;DR: What causes hypoglycemia?
Most often: too much insulin or diabetes medicine, not enough food, extra exercise, or alcohol. Less commonly: serious illness, hormone deficiencies, rare tumors, metabolic or liver problems, and in some people, an exaggerated insulin response after meals.

Information gathered from public forums or data available on the internet and portrayed here.