A blood sugar level below 70 mg/dL (3.9 mmol/L) is considered low. That’s the threshold the American Diabetes Association uses in its 2025 Standards of Care, and it applies whether you’re checking with a finger stick or a continuous glucose monitor. But not all lows are equal: how far below 70 you drop determines the severity and what you need to do about it.
The Three Levels of Low Blood Sugar
The ADA breaks hypoglycemia into three tiers based on how low glucose falls and how it affects your body.
Level 1 is a reading between 54 and 69 mg/dL (3.0 to 3.9 mmol/L). This is a mild low. Your body is still functioning normally, but it’s sending early warning signals that fuel is running short. Most people can treat this on their own with a quick snack.
Level 2 is anything below 54 mg/dL (3.0 mmol/L). At this point, your brain isn’t getting enough glucose to work properly. Thinking becomes foggy, coordination suffers, and the episode requires immediate action. This is a clinically significant low that needs fast-acting carbohydrates right away.
Level 3 is defined not by a specific number but by what’s happening to you: your mental or physical state is so impaired that you need someone else to help you recover. You may be confused, unable to swallow safely, or unconscious. This is a medical emergency regardless of what the meter reads.
What Low Blood Sugar Feels Like
The first symptoms you’ll notice are your body’s stress response kicking in. When glucose starts to drop, your system releases adrenaline to push stored sugar into your bloodstream. That causes shakiness, a racing heartbeat, sweating, and anxiety. You might feel suddenly hungry or notice tingling around your lips and fingertips. These warning signs typically show up in the Level 1 range and are your cue to eat something.
If blood sugar keeps falling into Level 2 territory, the symptoms shift. Instead of feeling jittery, you start to feel “off” mentally. Difficulty concentrating, slurred speech, blurred vision, and clumsiness are all signs your brain is running low on its primary fuel. Some people become irritable or argumentative without realizing why. Others describe it as feeling detached or dreamlike. At the most severe end, confusion gives way to seizures or loss of consciousness.
Not everyone gets obvious warning signs. People who experience frequent lows, especially those with long-standing diabetes, can develop what’s called hypoglycemia unawareness. Their body stops producing the early adrenaline surge, so the first symptom they notice is already a brain-related one like confusion. This makes regular monitoring especially important.
Low Blood Sugar While You Sleep
Nocturnal hypoglycemia is particularly tricky because you can’t feel the warning signs while asleep. Clues that it happened overnight include waking up drenched in sweat, having vivid nightmares, or feeling unusually tired and headachy the next morning. A partner might notice restless tossing, trembling, or sudden changes in your breathing pattern during the night. If you wake up with an unexpectedly high reading in the morning, that can also be a sign: your body sometimes overcompensates for a nighttime low by dumping stored sugar into your bloodstream before you wake.
Common Causes
For people with diabetes, the most frequent trigger is a mismatch between medication and food. Taking insulin or certain oral diabetes medications without eating enough, eating later than usual, or being more physically active than expected can all pull blood sugar down faster than the body can compensate. Alcohol adds another layer of risk because it blocks the liver’s ability to release stored glucose, sometimes for hours after drinking.
People without diabetes can also experience low blood sugar, though it’s less common. Reactive hypoglycemia causes a dip a few hours after eating, often after a meal heavy in refined carbohydrates. The body overproduces insulin in response to the sugar spike, and glucose crashes on the back end. Prolonged fasting, intense exercise without adequate fuel, and certain hormonal deficiencies (particularly low cortisol) can also drive blood sugar below normal. Rarely, a small tumor on the pancreas called an insulinoma produces excess insulin continuously.
How to Treat a Low
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 cycling through those steps until your level is back in your target range. Good sources of 15 grams of fast carbs include four glucose tablets, half a cup of juice or regular soda, or a tablespoon of honey.
What you choose matters. 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. Save the more substantial snack for after you’ve corrected the low, to keep it from dropping again.
For a Level 3 episode where the person can’t safely swallow or is unconscious, glucagon is the emergency treatment. It comes in two main forms: a nasal spray and an injection. The nasal version is a single puff into one nostril and requires no mixing or preparation, which makes it far easier for a bystander to use under pressure. In simulated emergencies, untrained people could successfully administer the nasal spray, while the injectable form almost always required prior training to use correctly. If you take insulin, keeping glucagon accessible and making sure the people around you know where it is (and how to use it) is worth the effort.
What Counts as Normal
For context, a healthy fasting blood sugar typically falls between 70 and 99 mg/dL. After meals, it’s normal for glucose to rise temporarily and then settle back down, usually staying below 140 mg/dL within two hours of eating. A reading in the 60s can happen in healthy people, particularly after prolonged exercise or an overnight fast, and isn’t always a problem if you feel fine. The 70 mg/dL cutoff is the point where most bodies start mounting a hormonal response to bring sugar back up, which is why it’s used as the clinical threshold.
If you’re seeing numbers below 70 regularly and you don’t take diabetes medication, that pattern is worth investigating. Occasional dips that resolve quickly with food are usually harmless, but repeated episodes with significant symptoms can point to an underlying cause that needs attention.