For people with diabetes, a blood sugar below 70 mg/dL (3.9 mmol/L) is considered low. That’s the threshold where symptoms can start and where you should take action to bring your levels back up. But not all lows are equal. Clinicians classify hypoglycemia into three levels, and understanding where you fall matters for knowing how urgently you need to respond.
The Three Levels of Low Blood Sugar
A Level 1 low falls between 54 and 69 mg/dL (3.0 to 3.9 mmol/L). This is the most common type, and most people can treat it on their own with fast-acting carbohydrates. You might feel shaky, hungry, or a little off, but you’re still able to think clearly and help yourself.
A Level 2 low drops below 54 mg/dL (3.0 mmol/L). At this point, your brain is running short on fuel, and symptoms become more intense. Confusion, difficulty speaking, and poor coordination are common. You can still sometimes treat this yourself, but the window is narrowing.
Level 3 is defined not by a specific number but by what’s happening to you: it’s any episode where you need someone else’s help to recover. You may be disoriented, unconscious, or unable to swallow safely. This is a medical emergency regardless of what the meter reads.
What Low Blood Sugar Feels Like
The earliest symptoms come from your body’s adrenaline response. Your hands shake, your heart pounds, you break into a sweat, and you feel suddenly, urgently hungry. Some people describe anxiety or a sense of dread that seems to come out of nowhere. Nausea and tingling in the lips or fingers can also show up at this stage.
If blood sugar keeps falling, symptoms shift from your body’s alarm system to your brain struggling for glucose. You might have trouble concentrating, slur your words, or feel unusually drowsy. Behavior changes are common, and people around you may notice before you do. You could become irritable, confused, or act in ways that seem out of character. At the most severe end, seizures and loss of consciousness can occur.
One tricky aspect: the specific number that triggers symptoms varies from person to person. Someone who runs high most of the time might feel shaky at 80 mg/dL, while someone with tightly controlled blood sugar might not notice anything until they’re well below 60.
Why Some People Stop Feeling the Warning Signs
About 25% of people with type 1 diabetes develop a condition called hypoglycemia unawareness, where the usual early warnings (shaking, sweating, hunger) fade or disappear entirely. An estimated 10 to 15% of people with type 2 diabetes who use insulin or certain oral medications experience it as well, and the real number may be higher.
The mechanism is straightforward but dangerous. Each time your blood sugar drops low, your body resets its alarm threshold a little lower. If yesterday you felt symptoms at 60 mg/dL, today you might not notice anything until you hit 55. The problem is that the glucose level triggering unconsciousness does not shift downward along with it. So the gap between “I feel fine” and “I’m unconscious” keeps shrinking until there’s almost no warning at all.
The good news is this process is partially reversible. Avoiding lows for several weeks can help restore your body’s ability to sense dropping blood sugar. Working with your care team to adjust medication timing and doses is the most common approach.
Lows During Sleep
Nearly half of all low blood sugar episodes happen at night, and more than half of severe episodes occur during sleep. That makes nighttime lows one of the bigger risks for people on insulin.
You or a partner might notice restless sleep, sweating or clammy skin, trembling, sudden changes in breathing pattern, nightmares, or a racing heartbeat. Some people wake up with a headache, feeling exhausted, or with damp sheets and no memory of anything unusual. The real concern is for people who sleep straight through without waking.
A continuous glucose monitor (CGM) with a low-glucose alarm is one of the most effective tools for catching nighttime lows. These devices check your glucose every few minutes and can wake you with an alert before levels drop into dangerous territory. Some newer systems paired with insulin pumps can also reduce or suspend insulin delivery automatically when a low is predicted.
How to Set CGM Alerts
Most people benefit from setting their low-glucose alert somewhere between 70 and 75 mg/dL. If your device offers predictive alerts, those can warn you 10 to 30 minutes before you actually reach your threshold, giving you time to act before symptoms start.
Certain situations call for more conservative settings. If you’re at higher risk from lows (older adults, people who drive professionally, anyone with hypoglycemia unawareness), setting the alert between 80 and 100 mg/dL adds a safety buffer. During exercise, a higher threshold is also useful because blood sugar can drop quickly with physical activity.
People who need tighter control, such as during pregnancy, may set their low alert slightly lower, around 65 to 70 mg/dL, and rely more heavily on predictive alerts to catch drops early. The key is finding a balance between catching real lows and avoiding so many notifications that you start ignoring them.
The 15-15 Rule for Treating a Low
The standard approach is simple: eat 15 grams of fast-acting carbohydrates, then wait 15 minutes and recheck your blood sugar. If you’re still below 70 mg/dL, eat another 15 grams and check again. Good options for those 15 grams include four glucose tablets, a small tube of glucose gel, four ounces of juice or regular soda, or a tablespoon of honey.
The waiting part matters. It’s tempting to keep eating when you feel terrible, but overtreating a low leads to a rebound spike that can send blood sugar soaring. Fifteen minutes is roughly how long it takes for simple sugar to reach your bloodstream and start working.
Once your blood sugar is back above 70, follow up with a small snack that includes some protein or fat if your next meal is more than an hour away. This helps stabilize levels and prevents another dip.
When Someone Else Needs to Help
A Level 3 low, where you can’t safely treat yourself, requires someone nearby to step in. If you’re conscious but confused, another person can help you drink juice or place glucose gel inside your cheek. If you’re unconscious or unable to swallow, food and liquid in the mouth create a choking risk, and glucagon is the appropriate treatment.
Glucagon comes in three forms today. A nasal spray delivers powdered glucagon through the nose in one step, with no needles and no mixing required. It works even if the person is unconscious. A pre-mixed pen works like an EpiPen: remove the cap, inject into the outer thigh, upper arm, or lower abdomen at a 90-degree angle. A traditional kit requires mixing a powder with liquid before injecting, which is more complicated under pressure. Whichever form is used, the person should be rolled onto their side afterward because nausea and vomiting are common side effects.
If you’re on insulin or medications that can cause lows, keeping glucagon accessible and making sure the people around you know where it is and how to use it is one of the most important safety steps you can take.