When blood sugar drops below about 70 mg/dL, your body launches a stress response that produces a cascade of symptoms, from mild shakiness to, in severe cases, seizures and loss of consciousness. What happens depends on how low your blood sugar goes, how quickly it falls, and how often you experience episodes.
How Your Body Responds to Falling Blood Sugar
Your brain runs almost entirely on glucose. When levels start to drop, sensors in your liver and brain detect the decline and trigger a hormonal alarm system. Your body releases glucagon (which tells the liver to dump stored sugar into the bloodstream), adrenaline, cortisol, and growth hormone. At the same time, insulin production drops. This coordinated response is your body’s attempt to push blood sugar back up on its own.
Adrenaline is responsible for the symptoms most people notice first. It’s the reason a low feels a lot like a panic attack: your heart races, your hands tremble, you break into a sweat. These warning signs are actually useful. They show up before the more dangerous effects set in, giving you a window to eat something and correct the drop.
Early Warning Signs
The first symptoms come from that adrenaline surge. They include sweating, palpitations, trembling, anxiety, hunger, dizziness, and a tingling feeling on the skin. Most people learn to recognize these quickly, especially if they take insulin or other diabetes medications that can push blood sugar too low. These symptoms can appear within minutes and tend to resolve just as quickly once you get some sugar into your system.
What Happens When Blood Sugar Drops Further
If blood sugar keeps falling and your brain doesn’t get the glucose it needs, a different set of symptoms takes over. These are caused directly by your brain running low on fuel, and they’re more serious. You may notice confusion, difficulty concentrating, irritability, trouble speaking clearly, or blurred vision. Some people experience weakness on one side of the body that can mimic a stroke. In the most extreme cases, untreated low blood sugar leads to seizures, loss of consciousness, and coma.
The progression matters: the adrenaline-driven symptoms (shaking, sweating, racing heart) typically come first and serve as an early warning. The brain-related symptoms (confusion, slurred speech, passing out) come later as glucose levels continue to decline. That gap between the two stages is your window to act.
Low Blood Sugar During Sleep
Nighttime lows are especially tricky because you can sleep right through the early warning signs. A bed partner might notice restless or irritable sleep, clammy skin, trembling, sudden changes in breathing pattern, or a racing heartbeat. Nightmares are common and sometimes intense enough to jolt you awake. If you wake up with a headache, feeling unusually tired, or with damp sheets from sweating, a nighttime low is a likely explanation.
Nocturnal episodes are concerning because they can go untreated for hours, and repeated overnight lows contribute to the long-term risks described below.
When Your Body Stops Warning You
One of the most dangerous things that can happen with low blood sugar is losing the ability to feel it coming. This is called hypoglycemia unawareness, and it develops in people who experience frequent lows. Each time blood sugar drops, the threshold that triggers warning symptoms shifts a little lower. Over time, you may not feel shaky or sweaty until your blood sugar is dangerously low, or you may skip the warning stage entirely and go straight to confusion or unconsciousness.
The critical problem, according to researchers at the NIDDK, is that while the symptom threshold keeps dropping, the threshold for losing consciousness does not. The gap between “I feel a little off” and “I’m unconscious” shrinks until it essentially disappears. This raises the risk of car accidents, falls, workplace injuries, and other situations where sudden impairment is dangerous for you and the people around you.
Long-Term Effects of Repeated Lows
A single mild low that’s treated quickly is unlikely to cause lasting harm. But recurrent episodes, especially severe ones, take a real toll on two major systems: the brain and the heart.
Repeated hypoglycemia is linked to cognitive decline over time, including problems with memory and processing speed. Severe episodes are also associated with cerebrovascular events like stroke. People who experience a severe low have a higher risk of heart attack or stroke in the following year.
The cardiovascular effects are particularly well documented. Low blood sugar can cause a heart rhythm disturbance called QT prolongation, which increases the risk of dangerous irregular heartbeats. The range of possible rhythm problems includes abnormally slow heart rate, atrial fibrillation, and ventricular tachycardia. In people with type 2 diabetes, the heart’s normal ability to adjust its rhythm in response to stress is already impaired, which means even mild lows can carry a higher-than-expected risk of sudden arrhythmia.
How to Correct a Low
The standard approach is the 15-15 rule recommended by the CDC: 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. Examples of 15 grams of fast-acting carbs include four glucose tablets, four ounces of juice, or a tablespoon of honey.
This works well for mild to moderate lows where you’re still alert enough to swallow safely. If someone is confused, unable to eat, or unconscious, they need help from another person, and in many cases emergency treatment with injectable glucagon. This is why people at risk for severe lows are often prescribed a glucagon kit and encouraged to make sure the people around them know how to use it.
Who Is Most at Risk
Low blood sugar is most common in people who take insulin or certain oral diabetes medications that stimulate insulin production. But it can also happen in people without diabetes due to prolonged fasting, heavy alcohol use, certain medical conditions affecting the liver or adrenal glands, or rarely, insulin-producing tumors. Intense exercise without adequate fuel is another common trigger, even in people who don’t have diabetes.
The risk is highest in people with type 1 diabetes, people with long-standing type 2 diabetes on insulin, older adults (who may have blunted symptom awareness), and anyone with a history of severe lows, since past episodes are the strongest predictor of future ones.