A low glucose reading means your blood sugar has dropped below the level your body needs to function normally, generally below 70 mg/dL. This can happen to people with diabetes as a side effect of medication, but it also occurs in people without diabetes due to diet, alcohol, or underlying health conditions. The experience ranges from mild shakiness you can fix with a snack to a medical emergency requiring outside help.
What Low Blood Sugar Feels Like
The symptoms of low blood sugar fall into two categories, and understanding the difference matters because they signal how serious the drop is.
The first wave of symptoms comes from your body’s stress response kicking in to raise blood sugar back up. These include sweating, a pounding or racing heart, trembling hands, sudden anxiety, and intense hunger. Most people recognize these signs and can act on them quickly.
If blood sugar continues to fall, your brain starts running short on fuel. This produces a different, more concerning set of symptoms: confusion, difficulty concentrating, irritability, slurred speech, and in rare severe cases, seizures or loss of consciousness. By this stage, you may not be thinking clearly enough to help yourself, which is why people around you need to know what’s happening.
Some people lose the ability to feel these warning signs altogether, a condition called hypoglycemia unawareness. Their blood sugar drops without the sweating, shaking, or hunger that would normally prompt them to eat. This is more common in people who experience frequent lows, because the body gradually stops triggering its alarm response.
Common Causes if You Have Diabetes
For people with diabetes, low blood sugar is most often a side effect of treatment. Insulin is the most common culprit, but several oral medications can also push glucose too low. Sulfonylureas and glinides directly stimulate insulin release and carry a well-known risk of lows. Some newer drug classes can contribute as well, particularly when combined with sulfonylureas.
The medication itself is rarely the whole story, though. A low typically happens when something throws off the balance between your medication dose and your body’s needs. The most common triggers are:
- Missing or delaying a meal after taking medication timed to cover food
- More physical activity than usual, which burns through glucose faster
- Drinking alcohol, which impairs your liver’s ability to release stored glucose
- Taking too much medication, whether by accident or miscalculation
Low Blood Sugar Without Diabetes
If you don’t have diabetes and your glucose comes back low, the explanation is sometimes straightforward and sometimes requires investigation. The two main patterns are reactive hypoglycemia and fasting hypoglycemia.
Reactive hypoglycemia happens within a few hours of eating, often after a meal heavy in refined carbohydrates. Your body overshoots its insulin response, pulling blood sugar down too far after the initial spike. The exact cause often isn’t clear, but it tends to improve with changes to meal composition, specifically eating smaller portions with more protein, fat, and fiber to slow glucose absorption.
Fasting hypoglycemia, where blood sugar drops after going without food for several hours, can point to something that needs medical attention. Possible causes include certain tumors that produce excess insulin (called insulinomas), inherited metabolic conditions, liver disease, or prior stomach surgeries like gastric bypass. Bariatric surgery changes how quickly food enters the small intestine, which can trigger exaggerated insulin surges after eating.
Alcohol is a factor for both groups. Even in people without diabetes, drinking on an empty stomach can suppress the liver’s glucose output enough to cause a significant drop.
Lows That Happen During Sleep
Nearly half of all low blood sugar episodes, and more than half of severe episodes, occur at night during sleep. This is especially common in people with type 1 diabetes taking long-acting insulin, but it can happen to anyone prone to lows.
Nocturnal lows are tricky because you’re asleep when the warning signs hit. Clues that it’s happening include waking up drenched in sweat, restless or irritable sleep, vivid nightmares, and noticeable changes in breathing pattern. A bed partner might notice trembling or a racing heartbeat. Waking up with a headache, feeling unusually groggy, or finding damp sheets are all signs worth investigating with a blood sugar check.
How to Treat a Low in the Moment
The standard approach is called the 15-15 rule: eat 15 grams of fast-acting carbohydrates, wait 15 minutes, then recheck your blood sugar. If it’s still below 70 mg/dL, repeat the process. Good sources of 15 grams include four glucose tablets, half a cup of juice or regular soda, or a tablespoon of honey.
The key word is “fast-acting.” Foods with fat or protein (like a candy bar or peanut butter) slow digestion and delay the glucose from reaching your bloodstream. Save the balanced snack for after your blood sugar has come back up, to keep it stable.
When a Low Becomes an Emergency
If someone with low blood sugar becomes confused, loses consciousness, or can’t swallow safely, they need emergency glucagon rather than food. Glucagon is a hormone that signals the liver to dump its stored glucose into the bloodstream, and it’s available in three forms: a nasal spray that delivers powdered glucagon through the nose, a pre-filled pen similar to an EpiPen that injects through clothing into the thigh or arm, and an older kit that requires mixing powder with liquid before injection.
The nasal spray is the simplest for bystanders to use since it requires no needles or mixing. If someone is unconscious after receiving glucagon, turn them on their side to prevent choking. They should regain consciousness within about 15 minutes.
For anyone who has experienced a severe low, having glucagon accessible and making sure the people around you know where it is and how to use it is not optional. It’s the difference between a scary episode and a dangerous one.
What a Low Reading Means on Lab Work
If your glucose came back low on routine blood work rather than a finger stick during symptoms, the context matters. A fasting glucose below 70 mg/dL on a single lab draw can reflect nothing more than a long gap since your last meal, especially if you fasted longer than the standard 8 to 12 hours before the test. Strenuous exercise the day before can also pull the number down temporarily.
A pattern of low readings, or a low reading paired with symptoms like shakiness, sweating, or confusion that resolve after eating, is more significant. Your doctor will typically want to confirm the finding with repeat testing and may check insulin levels alongside glucose to look for causes like excess insulin production. A single mildly low reading without symptoms is rarely cause for alarm on its own.