When blood sugar drops too low, your body loses its primary fuel source, triggering a cascade of symptoms that range from shaking and sweating to confusion, seizures, and loss of consciousness. For people with diabetes, low blood sugar (hypoglycemia) is generally defined as a reading below 70 mg/dL. For people without diabetes, it typically takes a drop below 55 mg/dL to cause problems.
Early Warning Signs
Your body has a built-in alarm system for low blood sugar. When glucose starts to fall, your nervous system fires off distress signals designed to get your attention and push you toward food. These early symptoms are driven by a rush of stress hormones, particularly adrenaline, and they feel a lot like anxiety: shaking hands, a racing heartbeat, sweating, and a gnawing hunger that comes on fast. You may also feel irritable, lightheaded, or notice tingling around your lips and fingertips.
These symptoms are uncomfortable, but they serve an important purpose. They’re your window to act before things get worse.
What Happens in Your Brain
Your brain runs almost entirely on glucose. Unlike your muscles, which can switch to burning fat for energy, your brain has very limited backup fuel options. So when blood sugar keeps falling, brain-related symptoms appear: difficulty concentrating, confusion, slurred speech, personality changes, blurred vision, and poor coordination. At this stage, your thinking becomes unreliable, which makes it harder to recognize and treat the problem yourself.
If blood sugar continues to drop without treatment, more serious neurological effects set in. Seizures can occur. Prolonged severe hypoglycemia can cause fainting, coma, brain injury, organ damage, or death. The American Diabetes Association notes that severe hypoglycemia is associated with a threefold increased risk of death.
Your Body’s Automatic Defense
Before symptoms even start, your body is already fighting back. A series of hormones kick in to raise blood sugar, working in a specific order of importance: glucagon comes first, followed by adrenaline, then growth hormone and cortisol. These hormones work primarily by signaling your liver to release stored glucose (glycogen) into the bloodstream. If those stores run low, your liver starts manufacturing new glucose from other raw materials like protein.
This defense system works well in most healthy people. But in people with diabetes, especially those who take insulin or certain medications, this counterregulatory response can become blunted over time, making low blood sugar episodes both more likely and more dangerous.
When You Stop Feeling the Warnings
One of the most dangerous complications of repeated low blood sugar is losing the ability to feel it coming. This condition, called hypoglycemia unawareness, develops because recurring episodes essentially train the body to stop sounding the alarm. The stress hormone response that normally creates those early warning signs (shaking, sweating, racing heart) becomes muted, so blood sugar can plummet to dangerous levels without any noticeable symptoms.
This creates a vicious cycle. Without warning signs, episodes go untreated longer, become more severe, and further blunt the body’s response to the next episode. People with hypoglycemia unawareness face a substantially higher risk of severe hypoglycemia because they lose the window where they could easily treat themselves.
Low Blood Sugar During Sleep
Hypoglycemia that happens overnight is particularly tricky because you’re not awake to notice the early signs. According to Johns Hopkins Medicine, signs of nocturnal hypoglycemia include restless or irritable sleep, hot and clammy skin, trembling, sudden changes in breathing patterns, nightmares, and a racing heartbeat. You might wake up with a headache, damp sheets, or a feeling of exhaustion that doesn’t match how long you slept.
A bed partner may notice these signs before you do. If you’re waking up regularly with these symptoms, it’s worth checking your blood sugar before bed and discussing the pattern with your care team.
Low Blood Sugar Without Diabetes
You don’t need to have diabetes to experience hypoglycemia. In people without diabetes, low blood sugar generally falls into two categories based on timing.
Reactive hypoglycemia happens within four hours after eating a meal. The exact cause often isn’t clear, though it can be linked to alcohol, previous gastric bypass surgery, or inherited metabolic conditions. Some people simply produce too much insulin in response to a carbohydrate-heavy meal, causing blood sugar to overshoot on the way down. Reactive hypoglycemia rarely drops glucose low enough to cause severe brain-related symptoms, but the shaking, sweating, and lightheadedness can still be disruptive.
Fasting hypoglycemia occurs when you haven’t eaten for an extended period. This type is less common and more likely to signal an underlying medical issue, such as a tumor that produces excess insulin, liver disease, or hormonal deficiencies.
Long-Term Risks of Repeated Episodes
A single mild episode of low blood sugar, treated quickly, is unlikely to cause lasting harm. But the picture changes with repeated or severe episodes. Prolonged hypoglycemia can cause brain injury, trigger abnormal heart rhythms, and is linked to increased mortality. The proposed mechanisms behind these cardiovascular risks include increased inflammation, a tendency toward blood clotting, damage to blood vessel walls, and electrical changes in the heart that predispose it to arrhythmias.
For people managing diabetes, preventing frequent lows matters just as much as avoiding highs. Both extremes carry real long-term consequences.
How to Treat a Low Blood Sugar Episode
The standard approach is called the 15-15 rule, recommended by the CDC: eat or drink 15 grams of fast-acting carbohydrates, wait 15 minutes, then recheck your blood sugar. If it’s still below 70 mg/dL, repeat the process until it returns to your target range. Young children, especially infants and toddlers, typically need less than 15 grams.
Good sources of 15 grams of fast-acting carbs include four glucose tablets, four ounces of juice or regular soda, or a tablespoon of honey or sugar. The key is choosing something that will hit your bloodstream quickly, not something with fat or protein that slows digestion (a candy bar, for instance, is a poor choice despite seeming like it would work).
For severe episodes where someone is unconscious or unable to swallow safely, emergency glucagon is the frontline treatment. Glucagon is available as a nasal spray or an injection and works by telling the liver to dump its stored glucose into the bloodstream. Several formulations exist, including auto-injectors approved for children as young as two and nasal sprays for ages four and up. If you take insulin, having an emergency glucagon kit accessible and making sure the people around you know how to use it can be lifesaving.