A blood sugar level below 70 mg/dL (3.9 mmol/L) is considered too low. At this point, your body doesn’t have enough glucose to function properly, and you need to act. A reading below 54 mg/dL (3.0 mmol/L) is more serious and requires immediate treatment to prevent dangerous complications like seizures or loss of consciousness.
The Three Levels of Low Blood Sugar
Low blood sugar, called hypoglycemia, is classified into three levels based on how far your glucose drops and how it affects you.
Level 1 (54 to 69 mg/dL): This is mild hypoglycemia. You’ll likely notice early warning signs like shakiness, sweating, or hunger. It’s a signal to eat something, but you can treat it on your own.
Level 2 (below 54 mg/dL): At this threshold, your brain starts running short on fuel. Confusion, difficulty speaking, blurred vision, and drowsiness can set in. This level requires immediate action.
Level 3 (any reading with altered mental or physical functioning): Severe hypoglycemia means you can’t treat yourself and need someone else’s help. This can happen at any glucose reading and may involve seizures or unconsciousness.
What Low Blood Sugar Feels Like
The earliest symptoms come from your body’s stress response: trembling, a pounding heart, sweating, anxiety, hunger, nausea, and tingling in your fingers or lips. These are your body’s alarm bells, driven by adrenaline, and they tend to appear first when glucose dips below 70 mg/dL.
If blood sugar keeps dropping, the symptoms shift. Your brain, which depends heavily on glucose, starts to struggle. You may have trouble concentrating, feel weak or drowsy, get a headache, have difficulty finding words, or notice your vision blurring. At this stage the situation is more urgent because your ability to recognize what’s happening and help yourself is fading.
How to Treat a Low Right Away
The standard approach is called 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 level is back in your target range, then follow up with a balanced snack or small meal that includes protein and carbohydrates to keep it stable.
Good options for those 15 grams include four glucose tablets, half a cup of juice or regular soda, or a tablespoon of honey. Glucose is the fastest-acting choice. Avoid foods with fat (like chocolate), which slow absorption and delay recovery.
If someone is unconscious or having a seizure, do not try to put food or liquid in their mouth. This is when an emergency glucagon kit matters. Glucagon is available as a nasal spray (a single puff into one nostril) and works even when the person can’t swallow. If there’s no response after 15 minutes, a second dose can be given. Call emergency services immediately. Anyone who takes insulin should have a glucagon kit prescribed and stored somewhere accessible, like a bedside drawer.
Causes in People With Diabetes
For people taking insulin or certain oral diabetes medications, low blood sugar is a well-known risk. Common triggers include taking too much medication, delaying or skipping a meal, exercising more than usual, or drinking alcohol. The timing of insulin matters too. A type of insulin called NPH, often taken at dinner, peaks six to eight hours later, which can cause blood sugar to drop in the middle of the night.
Exercise deserves special attention. Physical activity makes your muscles pull glucose from your bloodstream more efficiently, which can cause levels to drop during or after a workout. Research on endurance athletes found that even a small amount of carbohydrate during exercise (about 10 grams per hour) was enough to eliminate exercise-induced hypoglycemia and improve performance by 22%. If you take insulin, planning a snack before or during exercise can make a meaningful difference.
Low Blood Sugar Without Diabetes
You don’t need to have diabetes to experience hypoglycemia. Reactive hypoglycemia causes blood sugar to drop within four hours after eating, often after a meal high in refined carbohydrates. The exact mechanism isn’t always clear, but it appears to involve your body releasing too much insulin in response to a meal.
Other causes in people without diabetes include heavy alcohol use, certain inherited metabolic conditions, rare insulin-producing tumors, and prior gastric bypass or bariatric surgery (which changes how quickly food moves through your digestive system). If you’re experiencing repeated episodes of low blood sugar and don’t have diabetes, it’s worth getting a thorough evaluation to identify the underlying cause.
Hypoglycemia Unawareness
Some people, particularly those who have had diabetes for many years or experience frequent lows, gradually lose the ability to feel the early warning signs. This condition, called hypoglycemia unawareness, happens because repeated low episodes reset the body’s alarm system. If your blood sugar dropped to 60 mg/dL yesterday and triggered symptoms, your body may not sound the alarm today until it hits 55. Then 50. The threshold for symptoms keeps sliding lower.
The dangerous part is that the threshold for losing consciousness does not slide along with it. So the gap between “I feel fine” and “I’m unconscious” shrinks over time. This puts people at serious risk for car accidents, injuries at work, and other emergencies. Severe hypoglycemia also carries longer-term consequences: people who experience an episode of severe low blood sugar have a higher risk of heart attack or stroke in the following year.
If you suspect you’re losing awareness of your lows, a continuous glucose monitor can help by tracking your levels around the clock and alerting you when they start to fall.
Low Blood Sugar During Sleep
Nocturnal hypoglycemia is particularly tricky because you’re asleep when it happens and may not recognize the symptoms. Warning signs that a partner or family member might notice include restless sleep, sweating or clammy skin, trembling, sudden changes in breathing, a racing heartbeat, and nightmares.
Several factors raise the risk: skipping dinner, exercising close to bedtime, drinking alcohol in the evening, and taking certain insulin types that peak overnight. A continuous glucose monitor with a low-alarm feature can wake you if your levels drop, which is especially useful for people who experience frequent nighttime lows. Keeping a glucagon kit in the bedside drawer is a practical safety measure for anyone at risk.
Glucose Targets to Prevent Lows
The 2025 American Diabetes Association guidelines recommend that most adults with diabetes aim to spend more than 70% of their day with blood sugar between 70 and 180 mg/dL. Just as important, they recommend spending less than 4% of the day below 70 mg/dL, and less than 1% below 54 mg/dL. For older adults, the target is even stricter: less than 1% of time below 70 mg/dL.
Before meals, a typical target range is 80 to 130 mg/dL. After meals, the goal is to stay below 180 mg/dL. If you’re hitting these targets but still experiencing frequent lows, your medication regimen may need adjusting. Switching to a medication class with a lower risk of hypoglycemia, or reducing the dose of insulin or other high-risk medications, is a common strategy to break the cycle of repeated episodes.