A blood sugar level below 70 mg/dL (3.9 mmol/L) is generally considered low, a threshold recognized by the American Diabetes Association and used as the standard alert point in clinical practice. But not all low blood sugar is equally dangerous. The severity depends on how far below 70 your levels drop, how quickly they fall, and whether your body can still mount a normal recovery response.
The Three Levels of Low Blood Sugar
The American Diabetes Association classifies hypoglycemia into three levels based on glucose readings and how the episode affects you.
Level 1 is a reading between 54 and 69 mg/dL. This is a warning zone. Your body is running lower than it should, and you’ll likely notice early symptoms, but you can treat it yourself with food or a sugary drink. Most people at this level are still fully alert and functional.
Level 2 is a reading below 54 mg/dL (3.0 mmol/L). At this point, the brain is not getting enough fuel to work properly. Confusion, difficulty concentrating, blurred vision, and poor coordination become common. This level requires immediate action to raise blood sugar and carries real risk if ignored.
Level 3 is defined not by a specific number but by what’s happening to the person: they can’t function and need someone else’s help to recover. Blood sugar at this stage is often below 40 mg/dL. Seizures, loss of consciousness, and an inability to safely swallow food or drink can all occur. This is a medical emergency.
What Low Blood Sugar Feels Like
The symptoms of low blood sugar fall into two distinct categories, and they tend to appear in a predictable order. The first wave comes from your body’s stress response: sweating, shakiness, a pounding or rapid heartbeat, anxiety, and sudden intense hunger. These are your alarm signals, driven by adrenaline, and they typically show up when blood sugar first dips below 70 mg/dL.
If blood sugar keeps falling, the second wave hits. These symptoms come directly from the brain being starved of glucose: weakness, dizziness, trouble concentrating, confusion, and blurred vision. Behavior can change noticeably, sometimes to the point where others mistake the person for being drunk. In extreme cases, this progresses to seizures or loss of consciousness.
One complication worth knowing about: people who experience frequent low blood sugar episodes, particularly those on insulin, can develop something called hypoglycemia unawareness. The early warning symptoms (the sweating, shaking, and hunger) become blunted or disappear entirely, so the person skips straight to the dangerous brain-related symptoms without any advance notice.
Low Blood Sugar During Sleep
Blood sugar can drop below 70 mg/dL while you’re asleep, and you may not wake up to notice. Nocturnal hypoglycemia is especially common in people who take insulin, and the signs are easy to miss or misattribute. Your partner might notice restless sleep, sweating, trembling, sudden changes in breathing patterns, or a racing heartbeat. Nightmares are another hallmark, sometimes vivid enough to jolt the person awake.
Waking up with a headache, feeling unusually tired despite a full night’s rest, or finding damp sheets from sweating are all clues that blood sugar may have dropped overnight. If these patterns repeat, it’s worth checking your glucose levels before bed or using a continuous glucose monitor to track what happens while you sleep.
Low Blood Sugar Without Diabetes
Most people associate low blood sugar with diabetes medications, especially insulin, and that is the most common cause. But hypoglycemia can happen in people who don’t have diabetes at all.
Reactive hypoglycemia is one form, where blood sugar drops within four hours after eating a meal. It’s more common in people who have had stomach or bariatric surgery, which changes how quickly food moves through the digestive system and how the body releases insulin in response. But it can also occur without any surgical history.
Other causes in people without diabetes include severe liver disease, kidney disease, advanced heart disease, severe infections, prolonged starvation, and eating disorders like anorexia nervosa. When you go long stretches without eating, your body eventually burns through its stored glucose reserves and can no longer maintain normal blood sugar levels on its own. Certain medications unrelated to diabetes, and rarely, tumors that produce excess insulin, can also be responsible.
How to Treat a Low Blood Sugar Episode
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. Good options for those 15 grams include four glucose tablets, half a cup of juice or regular soda, or a tablespoon of honey or sugar.
The key word is “fast-acting.” You want something that hits your bloodstream quickly, not a complex meal with fat and protein that takes time to digest. A candy bar or a peanut butter sandwich won’t raise your blood sugar fast enough when it matters. Save the real meal for after your levels stabilize, which helps prevent another drop.
For severe episodes where the person can’t safely swallow, food and drink are not an option. Emergency glucagon, a hormone that signals the liver to release stored glucose, is the treatment. It’s available as an injection or a nasal spray, and anyone at risk for severe hypoglycemia should have it accessible, with the people around them knowing how to use it.
Continuous Glucose Monitors and Alert Thresholds
Continuous glucose monitors (CGMs) can be set to alert you before blood sugar drops to dangerous levels. Most major systems allow you to customize your low glucose alert somewhere between 60 and 100 mg/dL, depending on the device. The Dexcom G7 and Dexcom ONE+ offer the widest configurable range (60 to 150 mg/dL), while systems like the GlucoMen Day CGM use a tighter range of 60 to 80 mg/dL.
For most people, setting the alert at 70 mg/dL gives enough lead time to treat a drop before it becomes serious. If you experience hypoglycemia unawareness or frequent overnight lows, setting the alert higher (around 80 to 90 mg/dL) provides an extra buffer. The value of a CGM in this context is catching drops you wouldn’t otherwise feel, particularly during sleep or exercise.