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 to function normally, and you’ll likely start feeling symptoms like shakiness, sweating, or sudden hunger. A reading below 54 mg/dL (3.0 mmol/L) is a cause for immediate action, as the risk of confusion, loss of consciousness, and seizures rises sharply.
The Two Key Thresholds
Low blood sugar, called hypoglycemia, isn’t a single cutoff but a sliding scale of severity. The first threshold is 70 mg/dL. Below this number, your body releases stress hormones to try to push glucose back up, which produces the classic warning signs: trembling hands, a racing heart, sweating, anxiety, and nausea. You might also feel suddenly and intensely hungry. These symptoms are uncomfortable but serve as a useful alarm.
The second threshold is 54 mg/dL. Below this level, your brain is no longer getting enough fuel. Symptoms shift from physical discomfort to cognitive impairment: headache, blurred or double vision, confusion, difficulty speaking, and agitation. If blood sugar continues to fall without treatment, seizures and loss of consciousness can follow. In older adults, a severe drop can mimic stroke symptoms, including one-sided weakness and difficulty forming words, and it increases the actual risk of stroke or heart attack.
What Low Blood Sugar Feels Like
The symptoms tend to arrive in two waves. The first wave is driven by your body’s stress response. Your nervous system detects the drop and floods you with adrenaline, which causes sweating, warmth, palpitations, trembling, and a gnawing sense of anxiety. Some people also feel tingling in their lips or fingers. This stage is your window to act.
If blood sugar keeps falling, the second wave hits. This one comes from the brain itself running short on glucose. Thinking gets foggy. You may struggle to concentrate, slur your words, or feel disoriented. Vision can blur. At the most dangerous extreme, you may become combative or unresponsive, or have a seizure. People around you might notice these changes before you do, which is why it helps to let close friends, family, or coworkers know what low blood sugar looks like.
When You Stop Feeling the Warning Signs
Some people, especially those who experience frequent lows, lose the ability to feel that first wave of symptoms. This condition is called hypoglycemia unawareness, and it’s one of the most dangerous complications of repeated low blood sugar episodes. The mechanism is straightforward: each time your blood sugar drops low, your body recalibrates what it considers “low.” If you had symptoms at 60 mg/dL yesterday, today you might not notice anything until you hit 55. The threshold for feeling symptoms keeps shifting downward.
The critical problem is that the threshold for losing consciousness does not shift. So the gap between “I feel fine” and “I’m passing out” narrows until it essentially disappears. People with hypoglycemia unawareness can go from feeling normal to being unconscious with very little warning, which creates serious risks while driving, operating machinery, or simply being alone. Recurrent severe episodes are also linked to a higher risk of heart attack and stroke in the following year.
If you’ve noticed that you no longer feel your lows the way you used to, working with your care team to avoid hypoglycemia for several weeks can help reset your body’s alarm system.
Why Blood Sugar Drops Too Low
The most common cause is diabetes medication, particularly insulin or drugs that stimulate the pancreas to produce more insulin. Taking too much medication, skipping a meal, exercising harder than usual, or drinking alcohol on an empty stomach can all tip the balance toward a low.
But hypoglycemia also happens in people without diabetes. Reactive hypoglycemia causes blood sugar to drop within four hours after eating, typically because the body overshoots its insulin response to a meal. Fasting hypoglycemia, by contrast, occurs after prolonged periods without food and can signal an underlying issue like a hormone deficiency or, rarely, an insulin-producing tumor. Doctors confirm non-diabetic hypoglycemia using a set of criteria called Whipple’s triad: symptoms consistent with low blood sugar, a laboratory-confirmed low glucose reading at the time of symptoms, and resolution of those symptoms once blood sugar is raised.
How to Treat a Low in the Moment
The standard approach is the 15-15 rule. Eat or drink 15 grams of fast-acting carbohydrates, then wait 15 minutes for the sugar to reach your bloodstream. Good options include four glucose tablets, half a cup of juice or regular soda, or a tablespoon of honey. After 15 minutes, check your blood sugar again. If it’s still below 70 mg/dL, repeat with another 15 grams. Once your level is back to normal, eat a small snack or meal that includes protein and complex carbs to keep it stable.
The 15-15 rule works for mild to moderate lows where you’re alert and able to swallow safely. It does not work for severe episodes. If someone is too confused to eat, losing consciousness, unable to swallow, or not responding to repeated rounds of carbohydrates, they need glucagon. Glucagon is a hormone that signals the liver to release stored glucose. It comes in injectable and nasal spray forms, and anyone at risk for severe lows should have it on hand and make sure the people around them know where it is and how to use it.
Preventing Frequent Lows
If you take insulin or other blood sugar-lowering medication, consistent meal timing matters. Eating at roughly the same times each day, and not skipping meals, keeps your glucose supply steady against the medication working in your system. When you exercise, check your blood sugar before, during, and after activity, especially if the workout is longer or more intense than usual. A small carbohydrate snack before exercise can prevent a drop.
Alcohol deserves special attention. Your liver normally acts as a backup glucose source, releasing stored sugar when blood levels fall. Alcohol blocks this process, sometimes for hours after your last drink. That means a low can hit well after you’ve stopped drinking, including overnight while you sleep. Eating food alongside alcohol and checking your blood sugar before bed reduces this risk.
For people with reactive hypoglycemia who don’t take diabetes medication, the focus shifts to diet composition. Eating smaller, more frequent meals that pair carbohydrates with protein, fat, and fiber slows digestion and prevents the sharp insulin spike that triggers the post-meal crash. Cutting back on refined sugars and processed carbohydrates makes the biggest difference for most people.