When your blood sugar drops below 70 mg/dL, your body triggers a cascade of warning signals: shaking, sweating, a pounding heart, sudden hunger, and a wave of anxiety that seems to come from nowhere. These symptoms are your body’s alarm system, and if blood sugar continues to fall, the effects escalate from uncomfortable to dangerous, potentially causing confusion, seizures, loss of consciousness, and cardiac complications.
How Your Body Fights Back
Your body doesn’t just sit idle when blood sugar starts dropping. It launches a coordinated hormonal defense. The first response is a decrease in insulin production, the hormone that normally lowers blood sugar. Almost simultaneously, your pancreas releases glucagon, a hormone that signals your liver to dump its stored glucose into your bloodstream. If blood sugar keeps falling, your adrenal glands release adrenaline (epinephrine), which pushes even more glucose out of the liver and also restricts how much glucose your muscles and other tissues can absorb.
That adrenaline surge is what causes most of the early symptoms you feel: the shaking hands, racing heart, sweating, and jittery anxiety. These aren’t just side effects. They’re built-in warning signals designed to make you notice something is wrong and eat. Later, if blood sugar stays low, your body releases cortisol and growth hormone as backup, but these work more slowly and are less effective in the moment.
The Three Levels of Low Blood Sugar
Not all lows are equal. The American Diabetes Association classifies hypoglycemia into three levels based on severity.
Level 1 is a blood sugar between 54 and 70 mg/dL. This is the alert stage. You’ll likely notice the classic warning signs: shakiness, sweating, dizziness, irritability, and hunger. Most people can treat this on their own with a quick source of sugar.
Level 2 kicks in below 54 mg/dL. This is where the brain starts running short on fuel. Thinking becomes sluggish. You may feel confused, have trouble speaking clearly, or behave in ways that seem irrational to people around you. This level requires immediate action because your ability to help yourself is fading.
Level 3 is defined not by a specific number but by what’s happening to you: your mental or physical functioning is so impaired that you need someone else to help you recover. This can mean anything from being too confused to eat to having a seizure or losing consciousness entirely.
What Happens to Your Brain
Your brain is uniquely vulnerable to low blood sugar because, unlike your muscles, it can’t easily switch to burning fat for energy. It depends almost entirely on glucose. As blood sugar drops below roughly 45 mg/dL, confusion and delirium set in. The progression follows a predictable pattern: first slowed thinking and difficulty concentrating, then confusion and lethargy, then delirium, and finally seizures and coma.
At extremely low levels, below about 18 mg/dL, the brain’s energy reserves become depleted and electrical activity can flatline. Prolonged severe hypoglycemia at this level causes brain damage. In children whose brains are still developing, repeated severe episodes accompanied by seizures have been linked to subtle but measurable impairments in cognitive function years later.
Heart Risks During Severe Lows
Low blood sugar doesn’t just affect the brain. It puts real stress on the heart. The adrenaline surge that causes shaking and anxiety also drives up heart rate and widens pulse pressure. More concerning, blood sugar below 54 mg/dL is associated with cardiac arrhythmias, including dangerous changes to the heart’s electrical rhythm. These rhythm disturbances are driven partly by the adrenaline response and partly by a drop in blood potassium that accompanies hypoglycemia.
Severe hypoglycemia has been linked to roughly double the risk of subsequent cardiovascular events, including death. This association runs in both directions: people with cardiovascular disease are also more prone to severe lows, creating a reinforcing cycle of risk.
Low Blood Sugar During Sleep
One of the more unsettling aspects of hypoglycemia is that it can happen while you’re asleep and completely unaware. Nocturnal hypoglycemia occurs when blood sugar falls below 70 mg/dL during the night. Because you’re not awake to notice the usual warning signs, your body may struggle through a low for hours.
Signs that suggest overnight lows include waking up drenched in sweat, restless or irritable sleep, nightmares, trembling, sudden changes in breathing patterns, and a racing heartbeat that wakes you or your partner. Waking up with a headache, feeling unusually groggy, or finding damp sheets are also clues. If these symptoms happen regularly, it’s worth checking blood sugar levels during the night or discussing continuous glucose monitoring with your care team.
When Warning Signs Disappear
People who experience frequent low blood sugar episodes can develop a condition called hypoglycemia unawareness, where the body’s alarm system essentially stops working. The mechanism is surprisingly counterintuitive: repeated lows cause the brain to adapt to lower glucose levels, resetting the threshold at which it triggers the adrenaline-driven warning symptoms. Over time, the body’s hormonal response to falling blood sugar becomes blunted.
This creates a dangerous situation. Without the usual sweating, shaking, and anxiety to alert you, blood sugar can plummet into the severe range before you or anyone around you realizes something is wrong. The key driver is recurrent hypoglycemia itself. Each episode makes the next one harder to detect. The good news is that this process is at least partially reversible: carefully avoiding lows for a period of weeks can help restore some awareness, though it requires close monitoring and often adjustments to medication or insulin dosing.
How to Treat a Low
The standard approach is called the 15-15 rule. Eat or drink 15 grams of fast-acting carbohydrates, wait 15 minutes, then check your blood sugar again. If it’s still below 70 mg/dL, repeat. Keep going until your levels are back in your target range. Practical sources of 15 grams of carbs include four glucose tablets, four ounces of juice or regular soda, or a tablespoon of honey.
This approach works for Level 1 and most Level 2 episodes where you’re still alert enough to swallow safely. For Level 3 episodes, where someone is unconscious, seizing, or too confused to eat, oral carbohydrates are not safe because of the risk of choking. Emergency glucagon, which comes in injectable and nasal spray forms, is designed for exactly this situation. It works by signaling the liver to release its stored glucose, buying time until the person can eat or receive medical treatment. Anyone who takes insulin or medications that can cause lows should have glucagon available, and the people around them should know where it is and how to use it.
Who Is Most at Risk
Low blood sugar is most common in people with diabetes who take insulin or certain oral medications that stimulate insulin production. The risk is highest when meals are skipped or delayed, during or after exercise, after drinking alcohol, or when medication doses are too high. People with type 1 diabetes face the greatest risk because they depend entirely on external insulin, which doesn’t automatically adjust when blood sugar drops.
People without diabetes can also experience low blood sugar, though it’s far less common. Causes include prolonged fasting, excessive alcohol consumption, certain medications, and rarely, insulin-producing tumors or hormonal deficiencies. In people without diabetes, the body’s counterregulatory system is typically intact, so severe episodes are unusual. But when they do occur, the symptoms and consequences are the same.