Blood sugar below 70 mg/dL is considered low. Below 54 mg/dL is considered severely low and requires immediate action. These thresholds apply whether you have diabetes or not, though the causes and frequency of low blood sugar differ significantly between the two groups.
The Three Levels of Low Blood Sugar
The American Diabetes Association classifies hypoglycemia into three levels, each with increasing urgency:
- Level 1: Blood sugar between 54 and 69 mg/dL. This is below normal and needs correction, but you can typically treat it yourself.
- Level 2: Blood sugar below 54 mg/dL. This is clinically significant and requires fast-acting sugar immediately.
- Level 3: Any episode where your mental or physical state is so impaired that you need someone else’s help. This can mean confusion so severe you can’t feed yourself, loss of consciousness, or seizures. Level 3 is defined by the need for assistance, not a specific number on the meter.
For context, a normal fasting blood sugar sits between 70 and 100 mg/dL, and after meals it typically stays below 140 mg/dL. The target range for most adults with diabetes using a continuous glucose monitor is 70 to 180 mg/dL, and guidelines recommend spending less than 4% of the day below 70 and less than 1% below 54.
What Low Blood Sugar Feels Like
The symptoms tend to follow a predictable pattern as blood sugar drops. Early on, your body releases stress hormones to push glucose back up, which produces the first wave of warning signs: shakiness, sweating, a fast or pounding heartbeat, sudden hunger, anxiety, and pale skin. You might also notice tingling or numbness in your lips, tongue, or cheeks. These symptoms are uncomfortable but useful. They’re your body’s alarm system.
If blood sugar continues to fall, the brain starts running short on fuel. That’s when the symptoms shift from physical to cognitive: difficulty concentrating, confusion, slurred speech, blurry or tunnel vision, loss of coordination, and unusual behavior like being unable to complete simple tasks. At this stage, other people may notice something is wrong before you do.
Severe episodes can cause seizures or loss of consciousness. These are medical emergencies.
Low Blood Sugar While Sleeping
Nighttime drops are particularly tricky because you’re not awake to notice the early warning signs. Clues that it happened overnight include waking up drenched in sweat, having vivid nightmares, feeling unrested or irritable in the morning, or a partner noticing that you were trembling, breathing irregularly, or restless during the night. A racing heartbeat during sleep is another sign.
If you suspect overnight lows are happening regularly, a continuous glucose monitor can track your levels through the night and alert you when they drop.
Why Some People Stop Feeling the Warning Signs
Frequent low blood sugar episodes can blunt your body’s alarm response over time. This is called hypoglycemia unawareness, and it creates a dangerous cycle: the more lows you experience, the less you feel them coming, which makes you more likely to have severe episodes. Your body essentially recalibrates, treating lower and lower blood sugar levels as “normal” and delaying the stress hormone response that would otherwise warn you.
The good news is that this process is reversible. Carefully avoiding lows for several weeks can restore your body’s ability to sense them. This sometimes means accepting slightly higher blood sugar targets temporarily to break the cycle.
Causes Without Diabetes
Low blood sugar isn’t exclusive to people with diabetes, though it’s far more common in those taking insulin or certain diabetes medications. In people without diabetes, the most common pattern is reactive hypoglycemia, where blood sugar drops within four hours after eating. The exact cause often isn’t clear, but it’s linked to what and when you eat.
Other causes of low blood sugar in people without diabetes include alcohol consumption (especially on an empty stomach), prior stomach or bariatric surgery, inherited metabolic conditions, and rarely, certain types of tumors that affect insulin production. Prolonged fasting can also cause blood sugar to dip, though a healthy body is usually very good at maintaining glucose levels even without food for extended periods.
How to Treat a Low in the Moment
The standard approach is the 15-15 rule: eat or drink 15 grams of fast-acting carbohydrates, then wait 15 minutes and recheck your blood sugar. If it’s still below 70 mg/dL, repeat. Keep going until your levels return to your target range. Once they do, eat a balanced snack or small meal with protein and carbohydrates to keep them stable.
Fifteen grams of fast-acting carbs looks like four glucose tablets, a small tube of glucose gel, four ounces of juice, or a tablespoon of sugar or honey. Young children need less than 15 grams.
If someone is unconscious, seizing, or too confused to swallow safely, do not put food or liquid in their mouth. This is when emergency glucagon is used, a prescription product that rapidly raises blood sugar and can be given by a bystander. If glucagon is given and the person doesn’t improve enough to eat within an hour, or if symptoms don’t improve after eating, that’s a trip to the emergency room.
Why Repeated Lows Are Dangerous Long-Term
A single mild low that you catch and correct is not a health crisis. But repeated severe episodes carry real consequences. Prolonged low blood sugar can injure the brain, trigger dangerous heart rhythm disturbances, and is associated with increased risk of death. Studies in people with type 2 diabetes have found that severe hypoglycemia is one of the strongest predictors of major cardiovascular events, with the risk of death between 1.7 and 4.3 times higher in people who experience one or more severe episodes.
The mechanisms behind this are well documented: severe lows promote inflammation, increase blood clotting, impair blood vessel function, and place extra stress on the heart. That’s why current guidelines emphasize that avoiding lows is just as important as keeping blood sugar from running too high. If you’re experiencing frequent lows, it’s a signal that your treatment plan needs adjustment, whether that means changing medication types, adjusting doses, or modifying your eating patterns.