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 circulating in your bloodstream to fuel your brain and muscles properly. The medical term for this is hypoglycemia, and it ranges from a mild dip you can fix with a snack to a medical emergency that requires someone else’s help.
The Three Levels of Low Blood Sugar
Not all low blood sugar episodes are equal. Clinicians classify hypoglycemia into three levels based on how far your glucose drops and how it affects you:
- Level 1 (mild): Blood sugar is between 54 and 69 mg/dL. You’ll likely feel off, but you can treat it yourself.
- Level 2 (moderate): Blood sugar falls below 54 mg/dL. Symptoms become more intense and your thinking may be noticeably impaired.
- Level 3 (severe): Your blood sugar is so low that you can’t function normally. You need another person to help you recover.
Most people start noticing symptoms somewhere around 70 mg/dL, though the exact threshold varies. If you’ve had frequent low blood sugar episodes, your body can lose its ability to sound the alarm at those early levels, a dangerous condition where you skip straight from feeling fine to being confused or passing out.
What Low Blood Sugar Feels Like
The earliest signs are usually shakiness, dizziness, and pale skin. You might feel suddenly sweaty, anxious, or intensely hungry. Your heart may race. These symptoms happen because your body releases a surge of adrenaline trying to push your blood sugar back up, and adrenaline affects far more than just glucose.
If your blood sugar keeps dropping, the symptoms shift from physical to neurological. Your brain is the organ most dependent on a steady glucose supply, so when levels fall further you may have trouble speaking clearly, feel confused, struggle with coordination, or behave in ways that seem unusual to people around you. At this stage, you may not realize anything is wrong, which is part of what makes moderate and severe hypoglycemia so risky.
Low blood sugar can also happen while you sleep. The telltale signs include damp sheets from sweating, nightmares, and waking up feeling exhausted, irritable, or foggy. These nighttime episodes are easy to miss entirely unless someone else notices the sweating or restlessness.
Why Your Blood Sugar Drops
When your blood sugar starts falling, your body launches a coordinated hormonal response. First, your pancreas dials back insulin production and releases glucagon, a hormone that tells your liver to convert its stored glucose into usable fuel. At the same time, your adrenal glands pump out adrenaline, which does double duty: it triggers the liver to release even more glucose while also reducing how much glucose your muscles absorb. If the low persists, slower-acting hormones like cortisol kick in, shifting your body’s energy use away from glucose and toward burning fat instead.
This system works well in healthy people. The problem arises when something disrupts it. For people with diabetes, insulin or certain medications can lower blood sugar faster than the body’s defense system can compensate. Skipping a meal after taking insulin, exercising more than usual, or drinking alcohol can all tip the balance.
People without diabetes can experience low blood sugar too, though it’s less common. Reactive hypoglycemia causes a blood sugar drop within a few hours of eating, often without a clear medical explanation, though it seems linked to what and when someone eats. Other causes include heavy alcohol use, gastric bypass surgery, rare inherited metabolic conditions, and certain tumors that affect insulin production.
What Happens to Your Body During Severe Episodes
A brief, mild dip in blood sugar is uncomfortable but not dangerous. Severe or prolonged hypoglycemia is a different story. When your brain is starved of glucose for too long, it can sustain real injury. Brain imaging studies of people who experienced profound hypoglycemia show damage concentrated in specific areas: the basal ganglia (involved in movement), the hippocampus (critical for memory), the cerebral cortex (responsible for thinking and awareness), and the substantia nigra (which helps control movement). In the acute phase, the brain may swell. In the weeks and months that follow, brain atrophy, or shrinkage, can develop.
Some patients who survived severe prolonged episodes were left with lasting memory problems. Seizures and loss of consciousness are the most immediate dangers during an episode, and in rare cases, untreated severe hypoglycemia can be fatal.
How to Treat a Low Blood Sugar Episode
For mild to moderate episodes where you’re still alert and able to swallow, the standard approach is the 15-15 rule recommended by the CDC: eat or drink 15 grams of fast-acting carbohydrates, wait 15 minutes, then check your blood sugar again. If it’s still below 70 mg/dL, repeat. Good sources of 15 grams of fast-acting carbs include four glucose tablets, half a cup of juice or regular soda, or a tablespoon of honey.
The key word is “fast-acting.” You want sugar that hits your bloodstream quickly, not a complex meal with protein and fat that takes time to digest. Once your blood sugar stabilizes, follow up with a more substantial snack or meal to keep it from dropping again.
Severe episodes, where someone is unconscious, seizing, or too confused to eat safely, require a different response. Putting food or liquid in the mouth of someone who can’t swallow properly creates a choking risk. This is where emergency glucagon comes in. Glucagon is a prescription product that people with diabetes at risk of severe lows should keep on hand and make sure the people around them know how to use. It works by signaling the liver to dump its glucose stores into the bloodstream. If there’s no response after 15 minutes, a second dose can be given while waiting for emergency medical help.
Why Some People Stop Feeling the Warning Signs
One of the more dangerous complications of repeated low blood sugar is that your body gradually stops sounding the alarm. Normally, that rush of adrenaline at 70 mg/dL produces obvious symptoms: shaking, sweating, a pounding heart. But when your brain is exposed to low glucose levels over and over, it recalibrates what it considers “low.” The adrenaline response gets blunted, and you lose the early warning signs that would normally prompt you to eat something.
This is most common in people with type 1 diabetes or long-standing type 2 diabetes who have frequent hypoglycemic episodes. It creates a vicious cycle: without symptoms, you don’t catch the low early, it drops further, and each severe episode makes the unawareness worse. People in this situation often need to check their blood sugar more frequently or use a continuous glucose monitor that can alert them when levels start trending down.
Preventing Lows Before They Happen
If you take insulin or medications that can lower blood sugar, consistency matters. Eating on a regular schedule, checking your levels before and after exercise, and understanding how alcohol delays your liver’s ability to release glucose are all practical ways to reduce risk. Alcohol is particularly tricky because its effects on blood sugar can be delayed by hours, sometimes causing a low in the middle of the night.
For people with reactive hypoglycemia who don’t have diabetes, eating smaller, more frequent meals that include protein and fiber alongside carbohydrates can help prevent the rapid blood sugar spikes and crashes that trigger symptoms. Keeping a food diary to identify patterns in what triggers episodes is often one of the most useful first steps.
Anyone who has experienced a severe episode or who is losing awareness of their low blood sugar symptoms should make sure the people they live and work with know what hypoglycemia looks like and how to respond, including where emergency glucagon is stored and how to use it.