A low glucose level, called hypoglycemia, is a blood sugar reading below 70 mg/dL for people with diabetes or below 55 mg/dL for people without diabetes. At these thresholds, your body doesn’t have enough circulating fuel to power your brain and muscles normally, which triggers a cascade of warning symptoms that range from mild shakiness to confusion and loss of consciousness.
The Numbers That Define Low Blood Sugar
The American Diabetes Association breaks hypoglycemia into three levels of severity, each with a distinct blood sugar range and set of risks.
- Level 1: Blood sugar between 54 and 69 mg/dL (3.0 to 3.9 mmol/L). This is a warning zone. You can typically treat it yourself, but you need to act.
- Level 2: Blood sugar below 54 mg/dL (3.0 mmol/L). This is clinically significant and requires immediate treatment to prevent it from worsening.
- Level 3: A severe event where your mental or physical state is altered enough that you need someone else to help you. This is defined by the need for assistance, not by a specific number on a meter.
For people without diabetes, the threshold is lower because their bodies are better at self-correcting. A reading under 55 mg/dL is generally considered hypoglycemia in someone who doesn’t take diabetes medications.
What Low Blood Sugar Feels Like
Early symptoms come from your body’s stress response. When blood sugar drops, your system releases adrenaline to try to push glucose back into your bloodstream. That adrenaline surge causes shakiness, sweating, a racing heartbeat, and sudden hunger. You may feel anxious or irritable without an obvious reason.
If blood sugar continues to fall, symptoms shift from your body to your brain. Your brain is the most glucose-hungry organ you have, and when it runs short, you’ll notice confusion, difficulty concentrating, slurred speech, blurred vision, and coordination problems that can look like intoxication. At the most severe end, seizures and loss of consciousness are possible.
One dangerous complication is called hypoglycemia unawareness, where repeated low episodes train your body to stop sending those early warning signals. A cross-sectional survey published in Diabetes Care found that roughly 31% of people with type 1 diabetes had impaired awareness of hypoglycemia, even among those using continuous glucose monitors. Without the shakiness and sweating as an alarm, blood sugar can plummet to dangerous levels before anyone notices.
Common Causes
The most common reason for low blood sugar is a side effect of diabetes medications, particularly insulin. Too much insulin relative to the amount of food you’ve eaten or the exercise you’ve done pulls glucose out of your bloodstream faster than your body can replace it. People with type 2 diabetes who take sulfonylureas or meglitinides face elevated risk as well, because these medications stimulate the pancreas to release more insulin regardless of what your blood sugar is doing at the time.
Several everyday situations make an episode more likely: being more physically active than usual, skipping or delaying a meal, eating a meal without enough protein, fat, or fiber to slow digestion, and drinking alcohol without food. Alcohol is a particular risk because heavy drinking blocks the liver from releasing its stored glucose, cutting off your body’s main backup supply. Pregnancy during the first trimester can also increase hypoglycemia risk in people with type 1 diabetes due to hormonal shifts.
For people who don’t have diabetes, low blood sugar falls into two categories. Reactive hypoglycemia happens a few hours after eating, often because the body overshoots its insulin response to a carbohydrate-heavy meal. Fasting hypoglycemia occurs after prolonged periods without food and can signal an underlying condition like severe liver disease, kidney disease, advanced heart disease, or rarely a pancreatic tumor that produces excess insulin.
How to Treat an Episode
The standard approach is the 15-15 rule recommended by the CDC: 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 the cycle. Practical options for 15 grams of carbs include four glucose tablets, four ounces of juice, or a tablespoon of honey.
The key is speed and simplicity. Fat and protein slow digestion, so a candy bar or peanut butter crackers won’t raise your blood sugar as quickly as pure glucose or juice. Once your level stabilizes, eating a small balanced meal or snack helps prevent another drop.
Severe episodes, where someone is unconscious, seizing, or too confused to swallow safely, require a different response. Giving food or liquid to someone who can’t swallow properly creates a choking risk. This is when glucagon, an emergency medication that signals the liver to dump its glucose stores into the bloodstream, becomes necessary. Glucagon is available as a pre-filled auto-injector or injection kit and is given as a shot under the skin of the stomach, thigh, or upper arm. If you live with someone who uses insulin, having a glucagon kit accessible and knowing how to use it matters.
Low Blood Sugar While Sleeping
Nocturnal hypoglycemia is especially tricky because you’re not awake to notice the warning signs. Blood sugar below 70 mg/dL during sleep can cause restless or irritable sleep, sweating, trembling, sudden changes in breathing patterns, nightmares, and a racing heartbeat. A bed partner may notice these signs before you do. Waking up with a headache, feeling unusually tired, or finding damp sheets can all be clues that your blood sugar dropped overnight.
Prevention strategies typically involve adjusting the dose or timing of evening insulin, setting an early-morning alarm to test blood sugar and track how often drops occur, or wearing a continuous glucose monitor with a low-glucose alarm that can wake you before levels reach a dangerous point. A bedtime snack that includes protein and complex carbohydrates can also provide a slower, steadier source of glucose through the night.
Patterns Worth Paying Attention To
A single mild episode that responds to the 15-15 rule is common for people managing diabetes and isn’t necessarily alarming on its own. What matters more is the pattern. Frequent lows, lows that happen at the same time of day, or lows that are getting harder to feel all suggest that something in your medication, meal timing, or activity routine needs adjustment.
For people without diabetes who experience repeated symptoms of low blood sugar, the cause is worth investigating. Reactive hypoglycemia after meals can often be managed by shifting toward smaller, more frequent meals with balanced macronutrients. Fasting hypoglycemia that occurs without an obvious explanation, like skipping meals or heavy drinking, may point to a condition that needs medical evaluation.