Low blood sugar, called hypoglycemia, means the glucose in your bloodstream has dropped below the level your body needs to function normally. The standard threshold is below 70 mg/dL. Your brain runs almost entirely on glucose, so when levels fall too low, you feel it quickly: shaking, sweating, confusion, and irritability are all your body’s way of telling you to eat something now.
How Low Is Too Low
Not all low blood sugar is equally dangerous. The American Diabetes Association breaks it into three levels based on how far your glucose has dropped and how your body is responding.
- Level 1: Blood sugar between 54 and 69 mg/dL. You’ll likely feel early warning signs like shakiness or hunger, and you can treat it yourself.
- Level 2: Blood sugar below 54 mg/dL. This is clinically significant and needs immediate treatment. Brain function starts to suffer noticeably at this point.
- Level 3: A severe episode where you’re too confused, disoriented, or unconscious to treat yourself, regardless of the exact number on a meter. Someone else needs to help you.
What Happens Inside Your Body
Your body has a built-in rescue system for low blood sugar. When glucose starts dropping, the pancreas releases glucagon, a hormone that signals the liver to break down its stored sugar (glycogen) and push it into the bloodstream. At the same time, your adrenal glands release epinephrine (adrenaline), which does double duty: it tells the liver to produce even more glucose and temporarily blocks insulin from pulling sugar out of the blood.
That adrenaline surge is why low blood sugar feels so physical. The racing heart, sweating, and trembling aren’t the hypoglycemia itself. They’re your body’s emergency response kicking in. If the episode lasts longer, cortisol and growth hormone join in, making your tissues less responsive to insulin so that whatever glucose is available stays in the bloodstream longer.
This whole system works well in healthy people. Problems arise when these counter-regulatory hormones can’t keep up, either because glycogen stores are depleted, the liver is impaired, or medications are overriding the system.
Early Warning Signs vs. Brain Symptoms
The symptoms of low blood sugar come in two waves. The first wave is driven by that adrenaline response: shakiness, sweating, a pounding heart, hunger, tingling around the lips, and anxiety. These are your body’s alarm bells, and they typically show up when blood sugar dips into the 60s.
If glucose keeps falling, you get a second wave of symptoms that come directly from the brain not getting enough fuel. These include difficulty concentrating, slurred speech, blurry vision, confusion, clumsiness, and irritability that feels out of proportion to the situation. In severe cases, seizures or loss of consciousness can follow. The transition from “I feel off” to “I can’t help myself” can happen faster than people expect, which is why treating early symptoms right away matters so much.
Common Causes
If You Have Diabetes
The most common reason for low blood sugar is diabetes medication, particularly insulin or drugs that stimulate insulin production. Taking too much, eating less than planned, exercising harder than usual, or drinking alcohol can all tip the balance. Even a well-managed routine can produce occasional lows when any of these factors shift.
If You Don’t Have Diabetes
Hypoglycemia in people without diabetes is much less common, but it does happen. The causes generally fall into two categories.
Reactive hypoglycemia occurs within four hours of eating, usually after a meal heavy in sugar or processed simple carbohydrates like white bread or white pasta. Your body overproduces insulin in response, and blood sugar crashes on the other side. This is more of a pattern than a one-time event, and adjusting what you eat (more protein and fiber, fewer refined carbs) usually helps.
Fasting hypoglycemia happens when you haven’t eaten for an extended period. Severe liver disease, kidney disease, advanced heart disease, or serious infections can impair the body’s ability to maintain blood sugar on its own. Long-term starvation or eating disorders like anorexia can deplete glycogen stores entirely. Certain medications, including some used to treat malaria, can also lower blood sugar unexpectedly. In rare cases, a small tumor on the pancreas called an insulinoma produces excess insulin continuously.
The 15-15 Rule for Treating a Low
If your blood sugar is below 70 mg/dL and you can still eat and drink, the CDC recommends the 15-15 rule: eat 15 grams of fast-acting carbohydrates, wait 15 minutes, then check your blood sugar again. If it’s still under 70, repeat. Keep going until you’re back in your target range. Good options for 15 grams of carbs include four glucose tablets, half a cup of juice or regular soda, or a tablespoon of honey.
Once your blood sugar stabilizes, follow up with a balanced snack or small meal that includes protein and complex carbs. The fast-acting sugar gets you out of the danger zone, but it burns off quickly. Protein and slower-digesting carbs keep your levels steady afterward. Young children, especially infants and toddlers, typically need less than 15 grams per round, so their treatment amounts should be adjusted with a doctor’s guidance.
When Someone Can’t Treat Themselves
A Level 3 episode, where someone is too confused or unconscious to swallow safely, is a medical emergency. Never try to put food or liquid into the mouth of someone who isn’t fully alert, because of the choking risk. Emergency glucagon products are available that don’t require swallowing. A nasal glucagon powder delivers 3 mg into one nostril and can be given to adults and children over age one. If there’s no response after 15 minutes, a second dose can be administered. Call emergency services for any episode involving loss of consciousness.
Hypoglycemia Unawareness
One of the more dangerous complications of repeated low blood sugar is losing the ability to feel it coming. Normally, your body sends those adrenaline-driven warning signs (shaking, sweating, racing heart) when glucose drops to around 60 mg/dL. But if you experience frequent lows, the threshold for noticing symptoms keeps shifting downward. Yesterday you felt shaky at 60. Today you might not notice anything until you’re at 55. Tomorrow, maybe 50.
The problem is that the blood sugar level triggering unconsciousness doesn’t shift down with it. The gap between “I feel fine” and “I’ve passed out” gets dangerously narrow. People with hypoglycemia unawareness often describe not feeling low until they’re already in the 50s or lower. This is a significant risk factor for severe episodes and is worth discussing with a healthcare provider, especially if you’re on insulin. Continuous glucose monitors, which alert you to dropping levels before symptoms would normally kick in, are one of the most effective tools for managing this.
Preventing Repeated Episodes
If you’re dealing with occasional lows from diabetes medication, the most practical adjustments involve meal timing, exercise planning, and consistent monitoring. Eating before or soon after physical activity, keeping fast-acting carbs within reach, and checking your blood sugar before driving or sleeping all reduce risk. Alcohol lowers blood sugar for hours after drinking because it interferes with the liver’s ability to release glucose, so eating alongside any alcohol matters.
For reactive hypoglycemia without diabetes, dietary changes are the main strategy. Replacing sugary foods and refined carbs with meals built around protein, healthy fats, and fiber slows digestion and prevents the insulin overshoot that causes the crash. Eating smaller, more frequent meals rather than large ones with long gaps in between also helps keep glucose steady throughout the day.