Having low blood sugar means the glucose in your bloodstream has dropped below the level your body needs to function normally. For most people, that threshold is 70 mg/dL. When blood sugar falls below this point, your brain and muscles start running short on their primary fuel, triggering a cascade of warning signals designed to get you to eat something fast.
Low blood sugar, called hypoglycemia, is most common in people with diabetes who take insulin or certain medications. But it can happen to anyone under the right circumstances, and understanding what’s going on in your body helps you recognize it early and respond correctly.
What Happens in Your Body During a Drop
Your brain is the most glucose-hungry organ you have. It can’t store much fuel on its own, so it depends on a steady supply from your blood. When glucose levels start dipping below the normal range (around 65 to 70 mg/dL), your body launches a defense response before things get dangerous.
First, your pancreas releases a hormone called glucagon, which signals your liver to dump its stored glucose into your bloodstream. At the same time, your adrenal glands release adrenaline, the same hormone behind a fight-or-flight response. This is why low blood sugar can make you feel shaky, anxious, and sweaty even when nothing stressful is happening. These two hormones act fast and are the main drivers of recovery.
If glucose continues to fall, your body calls in backup. Growth hormone kicks in around 66 mg/dL, and cortisol (your stress hormone) around 58 mg/dL. These slower-acting hormones push your liver to produce new glucose from other sources like fat and protein. But the heavy lifting is done by glucagon and adrenaline, which can usually bring your levels back to normal on their own if you also eat something.
How Low Blood Sugar Feels
The symptoms come in two waves, driven by two different problems happening simultaneously: your body’s adrenaline surge, and your brain not getting enough fuel.
The adrenaline-driven symptoms tend to hit first. You might notice shaking or trembling in your hands, a pounding or racing heartbeat, sweating (especially clammy palms or a damp forehead), sudden intense hunger, and a wave of anxiety that seems to come out of nowhere. These symptoms are your body’s alarm system, and they’re useful because they warn you before things get serious.
If your blood sugar keeps dropping, the brain-related symptoms begin. These include difficulty concentrating, confusion, blurred vision, slurred speech, clumsiness, and feeling unusually drowsy or weak. At very low levels, you can lose consciousness or have a seizure. The distinction matters: the adrenaline symptoms are uncomfortable but not dangerous on their own, while the brain symptoms signal that you need to act immediately.
Common Causes in People With Diabetes
If you have diabetes and take insulin or medications that stimulate insulin production, low blood sugar is a known side effect. The most common triggers are straightforward: taking too much insulin, skipping or delaying a meal, exercising harder or longer than usual, or drinking alcohol (which blocks your liver’s ability to release stored glucose). Sometimes it’s a combination, like having an unusually active day and then eating dinner later than planned.
These episodes are particularly common at night. You might go to bed with normal blood sugar and drop while you’re asleep, especially after an active day or if you took too much insulin before bed. Nighttime lows can cause restless sleep, nightmares, heavy sweating, trembling, and changes in breathing. Some people wake up, but many sleep through it. A continuous glucose monitor can track your levels every few minutes and sound an alarm if you drop too low overnight.
Causes in People Without Diabetes
Low blood sugar isn’t exclusive to diabetes. Medications are the most common cause overall, but alcohol alone can do it, especially if you drink without eating. Your liver prioritizes breaking down alcohol over releasing glucose, so a few drinks on an empty stomach can leave your blood sugar dangerously low hours later.
Some people experience what’s called reactive hypoglycemia, where blood sugar drops two to four hours after eating a meal, particularly one high in refined carbohydrates. The body overshoots its insulin response, pulling glucose out of the blood too aggressively. This is different from fasting hypoglycemia, which happens after long periods without food and can signal an underlying medical issue.
Less common causes include hormone deficiencies (particularly cortisol), severe liver or kidney disease, sepsis, and rare tumors. An insulinoma, a small tumor in the pancreas, produces excess insulin and causes repeated low blood sugar episodes unrelated to meals or medication. Gastric bypass surgery can also cause hypoglycemia in some people, because food moves into the small intestine faster than normal, triggering an exaggerated insulin response.
Two Types: Reactive vs. Fasting
Reactive hypoglycemia shows up within a few hours of eating. It’s more common and often less severe. Many people with reactive hypoglycemia can manage it by eating smaller, more frequent meals, choosing complex carbohydrates over simple sugars, and pairing carbs with protein or fat to slow digestion.
Fasting hypoglycemia occurs after going without food for an extended period, sometimes overnight or longer. When it happens repeatedly, it warrants medical investigation because it’s more likely to point to an underlying condition like an insulinoma, hormone deficiency, or organ dysfunction. The diagnostic workup typically involves blood tests during a supervised fast to see how your glucose, insulin, and other hormones behave when you haven’t eaten.
How to Treat an Episode
The standard approach is called the 15-15 rule: 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. Keep going until your levels come back up. Good sources of 15 grams of carbs include four glucose tablets, four ounces of juice or regular soda, or a tablespoon of honey.
Once your blood sugar stabilizes, eat a proper meal or snack that includes protein and complex carbs to keep it from dropping again. The 15 grams of sugar you just consumed will be used up quickly, and without a follow-up meal, you could end up right back where you started.
For severe episodes where someone is confused, unconscious, or unable to swallow safely, emergency glucagon is the treatment. It’s available as a nasal spray (approved for ages 4 and up) or an injection. Both work by telling the liver to release its glucose stores. If you live with someone who takes insulin, keeping a glucagon kit accessible and making sure household members know how to use it is practical preparation that can prevent a trip to the emergency room.
When Warning Signs Stop Working
One of the more concerning complications of repeated low blood sugar is called hypoglycemia unawareness. Normally, your body sends those unmistakable adrenaline-driven warnings (shaking, sweating, racing heart) well before things get dangerous. But if you experience frequent lows, your body gradually recalibrates. The glucose level that triggers warning symptoms keeps getting lower and lower, until one day your blood sugar drops to a dangerous level and you feel nothing until you’re already confused or losing consciousness.
This tends to develop in people who have had diabetes for 20 or 30 years, those who aim for very tight glucose control, and people who have frequent hypoglycemic episodes. It also affects people with cognitive impairment, dementia, or depression, because these conditions make it harder to recognize and respond to subtle changes in how you feel.
The risks go beyond the immediate episode. People who lose consciousness from hypoglycemia can be injured in falls, car accidents, or workplace incidents. Recurrent severe episodes are also linked to long-term effects on brain and heart function. Research from NIDDK shows that a single episode of severe hypoglycemia raises the risk of heart attack or stroke in the following year. The good news: hypoglycemia unawareness can often be reversed by carefully avoiding all low blood sugar episodes for several weeks, which allows the body’s alarm system to reset.
Preventing Low Blood Sugar
If you take insulin or diabetes medications, the foundation of prevention is consistency: regular meals, predictable activity levels, and careful medication timing. Skipping meals is one of the most common and avoidable triggers. When your routine changes (more exercise, less food, alcohol), your medication may need to change too.
For nighttime lows specifically, eating a small snack before bed can help. If you drink alcohol in the evening, eating alongside it reduces the risk. Setting an early morning alarm to check blood sugar can help you identify patterns, and a continuous glucose monitor with a low-glucose alarm provides real-time protection while you sleep.
For people without diabetes who get reactive hypoglycemia, the strategy is dietary: smaller meals, fewer refined carbohydrates, more fiber and protein at each meal, and avoiding sugary drinks on an empty stomach. These changes slow the rate at which glucose enters and leaves your bloodstream, smoothing out the spikes and crashes that cause symptoms.