Low glucose, also called hypoglycemia, means your blood sugar has dropped below 70 mg/dL. At that level, your body doesn’t have enough readily available fuel, and you’ll typically start feeling symptoms like shakiness, sweating, and hunger. It can happen to people with diabetes as a side effect of treatment, but it also occurs in people without diabetes for a variety of reasons.
How Your Body Responds to Falling Blood Sugar
Your body has a built-in defense system that kicks in the moment blood sugar starts dipping. When glucose falls just below the normal range, around 65 to 70 mg/dL, your pancreas releases glucagon, a hormone that signals the liver to break down its stored sugar (glycogen) and release it into the bloodstream. At the same time, your adrenal glands pump out epinephrine (adrenaline), which pulls additional fuel from muscles and fat while also slowing down how quickly your tissues burn through glucose.
If low blood sugar persists, two slower-acting hormones join the effort: cortisol and growth hormone. These take longer to have an effect, but they help sustain glucose production over hours rather than minutes. Together, these four hormones form your counterregulatory system. When it works properly, blood sugar bounces back before you ever feel seriously impaired. Problems arise when this system is overwhelmed, blunted, or bypassed entirely.
What Low Blood Sugar Feels Like
Symptoms fall into two categories depending on what’s happening in your body. The first set comes from your nervous system’s alarm response: trembling, a pounding or racing heart, anxiety, sweating, and intense hunger. These are the early warning signs, driven by the same adrenaline surge your body uses to correct the drop.
The second set of symptoms comes from your brain actually running low on fuel. Because your brain depends almost entirely on glucose, even a modest shortfall can cause confusion, difficulty concentrating, fatigue, slurred speech, and changes in behavior. In severe cases, this progresses to seizures or loss of consciousness. Most people notice the adrenaline-type symptoms first, giving them time to act before the brain symptoms set in.
Low Blood Sugar While Sleeping
Nocturnal hypoglycemia is particularly tricky because you can’t recognize symptoms while asleep. Clues that it happened overnight include waking up drenched in sweat, soaked pajamas or sheets, restless sleep, nightmares, and feeling unusually tired, confused, or disoriented in the morning. Some people cry out during sleep without realizing it. If you’re waking up with unexplained headaches or fatigue regularly, overnight lows are worth investigating.
Common Causes in People With Diabetes
For people taking insulin or certain oral diabetes medications, low blood sugar is one of the most common side effects of treatment. The typical triggers are straightforward: taking too much insulin, eating less than planned, skipping or delaying a meal, or exercising more than usual without adjusting food intake or medication. Any mismatch between the amount of glucose-lowering medication in your system and the amount of food you’ve eaten can tip the balance.
Alcohol deserves special attention. Drinking on an empty stomach can cause blood sugar to drop quickly, and alcohol can also trigger delayed hypoglycemia hours later. This happens because alcohol interferes with the liver’s ability to produce new glucose. If you drink, pairing alcohol with food reduces the risk.
Causes in People Without Diabetes
Low blood sugar without diabetes is less common but does happen, and doctors generally divide it into two patterns based on timing.
Reactive (postprandial) hypoglycemia happens within a few hours of eating. It’s often related to an exaggerated insulin response after a meal. Possible underlying causes include overgrowth of insulin-producing cells in the pancreas, autoimmune conditions where the body makes antibodies against its own insulin, certain genetic mutations that affect how the body processes glucose, and prior stomach surgery that changes digestion speed and insulin timing.
Fasting hypoglycemia occurs when you haven’t eaten for an extended period. The most well-known cause is an insulinoma, a rare insulin-producing tumor of the pancreas that tends to cause weight gain because the excess insulin drives hunger. Other causes include other types of tumors (which more commonly cause weight loss), alcohol use, certain medications, liver disease, and inherited metabolic disorders like glycogen storage diseases, where the liver can’t properly release stored sugar. Disorders of fat metabolism and problems with gluconeogenesis, your body’s process for making new glucose from scratch, can also lead to fasting lows.
Hypoglycemia Unawareness
Some people, especially those who have had diabetes for many years or who experience frequent lows, gradually lose the ability to feel the early warning symptoms. This condition is called hypoglycemia unawareness, and it’s dangerous because by the time you or someone around you notices something is wrong, your blood sugar may already be severely low.
The mechanism behind it is essentially a recalibration problem. When your brain is exposed to repeated low blood sugar episodes, it adapts. The threshold at which your body triggers its alarm response shifts downward, meaning you need to be even lower before the sweating, shaking, and hunger kick in. The hormonal counterregulatory response also becomes blunted, with less glucagon and epinephrine released in response to each drop. This creates a vicious cycle: each unrecognized low makes the next one harder to detect.
The good news is that this process is at least partially reversible. Strictly avoiding hypoglycemia for a period of weeks can help restore awareness by resetting those thresholds. For people on insulin, this may mean adjusting the type of insulin used, since longer-acting insulin analogs with flatter, more predictable profiles tend to cause fewer sudden drops than older formulations. Continuous glucose monitors, which alert you when levels are falling, are also valuable tools for people who have lost their warning symptoms.
How to Treat a Low in the Moment
The standard approach is called the 15-15 rule. Eat or drink 15 grams of fast-acting carbohydrates, then wait 15 minutes and check your blood sugar again. If it’s still below 70 mg/dL, repeat with another 15 grams. Keep going until your level is back in your target range. Good sources of 15 grams of fast-acting carbs include four glucose tablets, 4 ounces of juice or regular soda, or a tablespoon of honey or sugar.
The key word is “fast-acting.” Foods with fat or protein, like a candy bar or peanut butter, slow digestion and delay the glucose from reaching your bloodstream. Save those for after you’ve corrected the low, when a more substantial snack can help keep your blood sugar stable.
Severe Lows and Emergency Treatment
When blood sugar drops so low that a person becomes confused, loses consciousness, or has a seizure, they can’t safely eat or drink. This is where glucagon comes in. Glucagon is a prescription hormone that rapidly signals the liver to dump stored sugar into the bloodstream.
It’s now available in several forms designed for non-medical people to use in an emergency. A nasal spray version requires no mixing or injection: you simply spray the powder into one nostril. There are also pre-filled auto-injectors, similar to the ones used for severe allergic reactions, that inject into the thigh. These options have made emergency treatment much more accessible compared to the older glucagon kits that required mixing a powder with liquid before injecting. If you live with someone who uses insulin or has a history of severe lows, knowing where their glucagon is kept and how to use it is worth the few minutes it takes to learn.