When your blood sugar drops below about 70 mg/dL, your body launches an emergency response to push it back up. First you’ll feel shaky, sweaty, and anxious as adrenaline floods your system. If levels keep falling, your brain starts running short on fuel, causing confusion, slurred speech, and eventually seizures or loss of consciousness. The speed and severity of this cascade depends on how low your blood sugar goes and how quickly you treat it.
Your Body’s Built-In Defense System
Your body doesn’t wait passively when blood sugar drops. It triggers a three-part counterattack. First, your pancreas dials back insulin production so less sugar gets pulled out of your bloodstream. Second, it ramps up a hormone called glucagon, which signals the liver to break down its stored sugar and release it into the blood. Third, your adrenal glands dump adrenaline (epinephrine) into your system, which further pushes the liver to release sugar while also raising your heart rate and sharpening your alertness.
This hormonal surge is essentially the same fight-or-flight response you’d get from a sudden scare, and it’s responsible for most of the symptoms you feel first. The shaking, the pounding heart, the sweating: those aren’t the low blood sugar itself hurting you. They’re your body’s alarm system going off.
The Early Warning Signs
The first symptoms are driven by that adrenaline release and tend to come on fast. You may notice:
- Shakiness or trembling in your hands
- A fast, thumping heartbeat
- Sweating, often cold and clammy
- Sudden anxiety or a feeling of dread
- Tingling, particularly around the lips and fingertips
- Intense hunger
These symptoms are uncomfortable, but they serve a purpose. They’re loud enough to get your attention so you eat something before things get worse. Most people who catch a low at this stage can correct it within minutes.
What Happens When Your Brain Runs Low
Your brain runs almost entirely on glucose. Unlike your muscles, which can switch to burning fat, the brain has no good backup fuel source. If blood sugar stays low or keeps dropping, a second wave of symptoms appears as the brain itself starts to struggle.
These symptoms look different from the adrenaline-driven ones. Instead of feeling wired and shaky, you feel foggy. Difficulty thinking, confusion, weakness, drowsiness, and a strange sense of warmth are common. Your speech may become slurred, and your coordination gets clumsy, which is why low blood sugar is sometimes mistaken for intoxication.
If levels continue to fall, the progression gets serious: disorientation gives way to stupor, then seizures, then loss of consciousness. At its most extreme, prolonged severe hypoglycemia can be fatal. Research from the National Institutes of Health has shown that severe episodes cause measurable damage to the brain’s cortex and hippocampus, the regions responsible for memory, learning, motor control, and reasoning. People who’ve experienced repeated severe lows can develop lasting deficits in memory, processing speed, and visual reasoning.
Low Blood Sugar During Sleep
One of the more unsettling aspects of hypoglycemia is that it can happen while you’re asleep, and you may not wake up for it. Nocturnal hypoglycemia sometimes reveals itself through night sweats, restless sleep, or waking with a headache and feeling unrested.
In more dramatic cases, people display bizarre behavior they don’t remember afterward. Clinical reports describe patients shouting, speaking nonsensically, walking around the room, ripping fixtures off walls, or becoming combative, all while essentially unconscious. One case involved a man who would suddenly start laughing, clapping his hands, and crossing his legs in strange patterns during early morning hours. These episodes resolved once blood sugar was corrected, but the people involved had no memory of them. If a bed partner notices unusual nighttime behavior, low blood sugar is worth investigating.
Common Causes
For people with diabetes, the most frequent trigger is too much insulin or other blood-sugar-lowering medication relative to how much they’ve eaten or how active they’ve been. Skipping a meal, exercising harder than usual, or miscalculating a dose can all tip the balance.
But low blood sugar also happens to people without diabetes. The most common causes include:
- Reactive hypoglycemia, where blood sugar drops a few hours after eating, often because the body overproduces insulin in response to a carbohydrate-heavy meal
- Alcohol, which blocks the liver’s ability to release stored glucose, especially on an empty stomach
- Medications, including certain antibiotics, blood pressure drugs, and lithium
- Liver or kidney disease, which impairs the body’s ability to regulate glucose
- Adrenal or pituitary gland problems, which disrupt the hormones that normally raise blood sugar
- Bariatric surgery, which changes how quickly food moves through the digestive system and can cause exaggerated insulin spikes
Rare causes include insulin-producing tumors of the pancreas (insulinomas), severe infections, and autoimmune conditions where the body produces antibodies that mimic insulin.
How to Treat a Low in the Moment
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. Examples of 15 grams of fast-acting carbs include four glucose tablets, four ounces of juice, or a tablespoon of sugar dissolved in water. You want something that hits the bloodstream quickly, so candy bars or cookies with fat and protein are less ideal since they digest more slowly.
Once your blood sugar comes back up, eat a small snack or meal with some protein and complex carbs to keep it stable.
When Someone Can’t Treat Themselves
If a person is unconscious, having a seizure, or unable to swallow, they can’t safely eat or drink anything. This is when emergency glucagon comes in. Glucagon is a hormone that tells the liver to dump its sugar stores into the bloodstream, and it works fast.
It’s available in several forms: nasal sprays that require no inhalation (you just spray the powder into one nostril), pre-filled auto-injectors that work like an EpiPen, and traditional injection kits. The nasal spray is approved for ages four and up, while most injectable options are approved for ages two and up. If you live with someone at risk for severe lows, having one of these on hand and knowing how to use it matters. The person will typically regain consciousness within 10 to 15 minutes, though they’ll likely feel nauseous afterward.
When You Stop Feeling the Warnings
Some people, particularly those with diabetes who’ve had frequent lows, gradually lose the ability to feel the early adrenaline-driven warning signs. This is called hypoglycemia unawareness, and it’s one of the more dangerous complications of repeated episodes.
Here’s what happens: when your brain is exposed to low blood sugar over and over, it starts to adapt. It resets its glucose-sensing threshold lower, essentially recalibrating what it considers “normal.” At the same time, your adrenaline response becomes blunted. After repeated lows, the body produces significantly less adrenaline in response to falling blood sugar. Without that adrenaline surge, you don’t get the shaking, sweating, and racing heart that would normally alert you. The first sign of trouble may be confusion or loss of consciousness, skipping the early warnings entirely.
The condition is partially reversible. Carefully avoiding any hypoglycemic episodes for several weeks can help restore the body’s sensitivity, gradually resetting the alarm system back to a higher, safer threshold. This often requires loosening blood sugar targets temporarily, which is a trade-off that’s worth discussing with a care team for anyone who has stopped noticing their lows.