Low blood sugar, called hypoglycemia, typically causes a recognizable cluster of symptoms: shaking, sweating, a racing heartbeat, and sudden hunger. A blood sugar reading below 70 mg/dL confirms it. But the signs can vary depending on how low your levels drop, whether it happens during the day or while you sleep, and whether you have diabetes or not.
The First Signs Your Body Sends
When blood sugar starts to fall, your body releases stress hormones to try to push it back up. Those hormones are what produce the earliest warning signs. You may notice shaking or trembling in your hands, a sudden cold sweat, a fast or pounding heartbeat, and a wave of anxiety or nervousness that seems to come out of nowhere. Intense hunger and dizziness are also common in this early stage.
These symptoms tend to come on quickly, sometimes within minutes. They’re your body’s built-in alarm system, and they usually appear when blood sugar drops below about 70 mg/dL. Most people who’ve experienced a low before learn to recognize the pattern: that distinctive combination of jitteriness, sweating, and an urgent need to eat something feels different from ordinary hunger or everyday stress.
What Happens When It Drops Further
If blood sugar continues to fall and your brain doesn’t get enough glucose, a second set of symptoms appears. These are more serious because they reflect the brain itself running short on fuel. Confusion, difficulty concentrating, slurred speech, weakness, and extreme fatigue are hallmarks of this stage. Some people describe feeling unusually warm or foggy-headed, and their behavior may seem off to others before they notice it themselves.
At very low levels, severe cognitive failure, seizures, and loss of consciousness can occur. These are medical emergencies. The progression from early warning signs to brain-related symptoms doesn’t always happen gradually. In some cases, especially if you’ve had frequent lows, the early warning stage can be muted or missing entirely, which means the first sign of trouble is confusion or disorientation rather than shaking or sweating.
Low Blood Sugar While You Sleep
Nighttime lows are tricky because you can’t feel the warning signs while you’re asleep. Instead, the clues show up differently. You or a partner might notice restless, irritable sleep, hot or clammy skin, trembling, nightmares, or sudden changes in breathing. A racing heartbeat during sleep is another red flag.
Waking up with a headache, feeling unusually tired despite a full night’s rest, or finding your sheets damp with sweat can all point to a low that happened overnight. If these signs keep recurring, it’s worth checking your blood sugar before bed and, if possible, during the night.
How to Confirm It With a Test
Symptoms alone aren’t enough for a definitive answer. A formal diagnosis of hypoglycemia requires three things happening together: you have symptoms, a blood sugar reading below 55 mg/dL (or below 70 mg/dL for people with diabetes), and those symptoms go away once your blood sugar comes back up. This three-part check, known as Whipple’s triad, is what clinicians use to confirm the diagnosis.
A fingerstick glucose meter gives you a real-time reading from a drop of blood. If you wear a continuous glucose monitor (CGM), keep in mind that these devices measure glucose in the fluid between your cells, not directly in your blood. During meals or exercise, that reading can lag behind your actual blood sugar by roughly 10 to 12 minutes. So if your CGM shows a normal number but you feel shaky and sweaty, a fingerstick can give you a more accurate snapshot of what’s happening right now.
Why Some People Lose Their Warning Signs
If you experience frequent low blood sugar episodes, your brain can gradually adapt to running on less glucose. Over time, it resets the threshold at which it triggers those early alarm signals, pushing it lower and lower. The result is a condition called hypoglycemia unawareness: your blood sugar drops, but you don’t feel the shaking, sweating, or racing heart that would normally alert you.
This happens because repeated lows dampen the release of stress hormones like epinephrine (adrenaline). Normally, falling blood sugar triggers a surge of epinephrine that produces the classic symptoms. After frequent lows, that surge weakens significantly. Changes in brain chemistry also play a role. Repeated episodes increase levels of an inhibitory brain chemical that essentially quiets the brain’s glucose-sensing alarm. The brain stops reacting to drops that would have triggered a strong response before.
Hypoglycemia unawareness is most common in people with long-standing type 1 diabetes or anyone who has had many hypoglycemic episodes in a short period. The good news is that carefully avoiding lows for several weeks can partially restore awareness by allowing the brain’s glucose-sensing thresholds to reset upward.
Low Blood Sugar Without Diabetes
You don’t need to have diabetes to experience hypoglycemia. In people without diabetes, low blood sugar generally falls into two categories based on when it happens.
Reactive (postprandial) hypoglycemia happens within a few hours after eating, especially after a high-carbohydrate meal. Your body overshoots on insulin, driving blood sugar too low. This is particularly common after gastric bypass surgery, where the altered digestive tract changes how quickly food is absorbed and how much insulin is released in response. It can also occur in people whose insulin-producing cells are overactive.
Fasting hypoglycemia happens when you haven’t eaten for an extended period. Alcohol is a common trigger because it blocks the liver’s ability to produce and release stored glucose. Liver or kidney disease can have a similar effect by reducing the body’s glucose reserves. Adrenal or pituitary gland problems can cause it too, since the hormones those glands produce help regulate blood sugar production and insulin sensitivity. Certain medications, including some blood pressure drugs and antibiotics, can also lower blood sugar as a side effect.
Exercise-related hypoglycemia is a third, less common category. For most people, blood sugar stays stable during physical activity, but certain genetic conditions and medication interactions can cause it to drop during or after a workout.
What to Do When It Happens
If you suspect your blood sugar is low and you’re able to eat or drink, follow the 15-15 rule: consume 15 grams of fast-acting carbohydrates, then wait 15 minutes and check your blood sugar again. If it’s still below 70 mg/dL, repeat the process. Good sources of 15 grams of carbs include four glucose tablets, four ounces of juice or regular soda, or a tablespoon of honey.
The key is choosing something that will raise blood sugar quickly. Foods with fat or protein, like a candy bar or peanut butter, slow digestion and won’t bring levels up as fast. Once your blood sugar is back above 70 mg/dL, eating a small snack or meal with some protein and complex carbs helps keep it stable.
If someone is unconscious or unable to swallow safely, they need emergency help. This is not a situation where food or juice can be given by mouth. Injectable or nasal glucagon, if available, is the appropriate response while waiting for medical assistance.
Patterns Worth Paying Attention To
A single episode of mild low blood sugar after skipping a meal or exercising hard isn’t necessarily a sign of a bigger problem. But recurring episodes, lows that happen without an obvious trigger, or symptoms that consistently appear at specific times (always in the early morning, always two hours after meals) suggest something worth investigating. Keeping a simple log of when symptoms occur, what you ate beforehand, and any blood sugar readings you capture gives your doctor concrete information to work with rather than vague descriptions of “feeling off.”