Low blood sugar, called hypoglycemia, is when your blood glucose drops below 70 mg/dL. At that level, your body doesn’t have enough readily available fuel, and you’ll start to feel symptoms like shakiness, sweating, and dizziness. While most common in people with diabetes, low blood sugar can happen to anyone under certain circumstances.
Normal blood sugar before a meal falls between 80 and 130 mg/dL. Once it dips below 70, your brain and body begin signaling that something is wrong. The lower it goes, the more serious the symptoms become.
Early and Late Warning Signs
Low blood sugar tends to announce itself in stages. The first signs are your body’s stress response kicking in: shakiness, sweating, a fast or irregular heartbeat, dizziness, sudden hunger, and trouble concentrating. Your skin may look noticeably pale. These early symptoms are your cue to act, because the next stage is harder to manage on your own.
If blood sugar keeps falling without treatment, the brain starts running short on glucose. That leads to confusion, slurred speech, clumsiness, and behavior that seems “off,” like being unable to finish a simple task. At its most severe, hypoglycemia can cause fainting, seizures, or coma. Left untreated long enough, it can cause brain damage or be fatal. This progression from mild shakiness to a medical emergency can happen in minutes, which is why recognizing those early signals matters so much.
What Causes Low Blood Sugar
For people with diabetes, the most common cause is too much insulin or other blood sugar-lowering medication relative to how much food they’ve eaten or how active they’ve been. Skipping a meal, eating less than planned, or exercising more than usual can all tip the balance. Alcohol makes things worse by impairing the liver’s ability to release stored glucose.
People without diabetes can experience low blood sugar too, though it’s less common. Reactive hypoglycemia causes blood sugar to drop within four hours after eating, and in many cases the exact reason isn’t clear. Other causes in non-diabetics include bariatric surgery (which changes how quickly food moves through the digestive system), inherited metabolic conditions, certain tumors, and heavy alcohol use.
The 15-15 Rule for Treatment
If you check your blood sugar and it’s below 70 mg/dL, the CDC recommends the 15-15 rule: eat 15 grams of fast-acting carbohydrates, wait 15 minutes, then check again. If it’s still under 70, repeat the process until you’re back in a safe range.
Good options for those 15 grams include:
- 4 ounces (half a cup) of juice or regular soda
- 1 tablespoon of sugar, honey, or syrup
- 3 to 4 glucose tablets
- 1 tube of glucose gel
- Hard candies or jellybeans (check the label for the right amount)
Young children, especially infants and toddlers, typically need less than 15 grams. The key is using simple sugars that absorb quickly. A candy bar or peanut butter crackers won’t work as fast because fat and protein slow digestion.
Severe Lows and Emergency Glucagon
When blood sugar drops low enough that a person becomes confused, loses consciousness, or can’t swallow safely, they need glucagon, a hormone that tells the liver to dump stored sugar into the bloodstream. You can’t give food or drink to someone who’s passed out or too confused to swallow, so glucagon is the bridge treatment until emergency help arrives.
Three forms of glucagon are currently available. A nasal spray delivers powdered glucagon through the nose in one step, with no needles involved, making it the easiest option for a panicked bystander. A pre-mixed pen works like an EpiPen: you remove the cap, press it against the outer thigh, upper arm, or lower stomach, and inject. A traditional kit requires mixing powder with liquid before drawing it into a syringe. For any of these, roll an unconscious person on their side afterward to prevent choking if they vomit.
If you live with someone who takes insulin, both of you should know where the glucagon is stored and how to use it before an emergency happens.
Low Blood Sugar During Sleep
Nighttime lows are particularly tricky because you’re asleep when the warning signs hit. You might not realize it happened until morning, when you notice damp sheets from sweating, a headache, unusual tiredness, or a paradoxically high blood sugar reading (your liver may have released a surge of glucose in response to the overnight low). Nightmares can also be a sign.
To reduce the risk, check your blood sugar before bed and aim for a reading between 90 and 150 mg/dL. If you exercised that day, ate less than usual, skipped dinner, or had alcohol, you’re at higher risk and a bedtime snack can help. Keep glucose tablets or juice on your nightstand so you can treat a low without stumbling to the kitchen. A continuous glucose monitor with low alerts can also catch drops while you sleep.
Exercise and Delayed Lows
Physical activity makes your muscles more sensitive to insulin, which is generally a good thing, but it means blood sugar can drop during a workout and for up to 24 hours afterward. That delayed effect catches people off guard. You might finish a long hike feeling fine and then have a low at 2 a.m.
Checking blood sugar more often before, during, and after exercise helps you spot patterns. A small snack before activity, or an adjustment to medication timing, can prevent exercise-related lows. For long-duration exercise like distance running or cycling, you may need both. The goal isn’t to avoid exercise. It’s to learn how your body responds so you can plan around it.
When Your Body Stops Warning You
Some people with diabetes lose the ability to feel low blood sugar coming on, a condition called hypoglycemia unawareness. It happens when repeated episodes of low blood sugar essentially train the body to stop sending alarm signals. The shakiness, sweating, and racing heart that normally serve as early warnings become muted or disappear entirely. Without those cues, blood sugar can plummet to dangerous levels before anyone notices.
This creates a vicious cycle: each unrecognized low makes the next one harder to detect, leading to more frequent severe episodes. The condition is more common in people who’ve had diabetes for many years or who experience frequent lows. Continuous glucose monitors are especially valuable for people with hypoglycemia unawareness, since the device can alarm even when the body doesn’t. Carefully avoiding lows for several weeks can sometimes restore some of the body’s natural warning response.