When your blood sugar drops below about 70 mg/dL, your body launches a rapid hormonal defense to push it back up, and you feel the effects almost immediately. Shakiness, sweating, a racing heart, confusion, and irritability are all part of that response. Most episodes are mild and easy to fix with a quick source of sugar, but severe or repeated lows can affect your heart, your brain, and your ability to detect future drops.
Your Body’s Emergency Response
Your body has glucose sensors in several places, including the liver, the brain, and even the carotid arteries in your neck. When these sensors detect falling blood sugar, they trigger a cascade of hormones designed to dump stored glucose back into your bloodstream. First, your pancreas releases glucagon, which tells the liver to convert its glycogen stores into glucose. At the same time, your adrenal glands release adrenaline (also called epinephrine), which speeds up the process and is responsible for many of the physical symptoms you feel. If blood sugar stays low, cortisol and growth hormone kick in to keep glucose production going over a longer period.
Insulin secretion also drops. This two-sided response, less insulin plus more counter-hormones, is your body’s best attempt to correct the problem on its own. In a healthy person, it usually works. But if you take insulin or certain diabetes medications, the correction may not be enough, and blood sugar can keep falling.
What Low Blood Sugar Feels Like
The symptoms fall into two categories based on what’s causing them. The first group comes from your nervous system reacting to the adrenaline surge. These are the symptoms you notice earliest:
- Shaking or trembling
- Sweating, especially clammy skin
- A pounding or racing heartbeat
- Hunger, often sudden and intense
- Anxiety or nervousness
The second group happens because your brain isn’t getting enough fuel. The brain runs almost entirely on glucose, so it’s one of the first organs affected. These symptoms tend to appear as blood sugar drops further:
- Difficulty concentrating or thinking clearly
- Confusion or unusual behavior
- Headache and fatigue
- Blurred vision
- Slurred speech
At very low levels, the brain symptoms become severe. Seizures, loss of consciousness, and coma are possible if blood sugar isn’t corrected. These outcomes are rare in mild episodes but represent a real danger in severe hypoglycemia.
What Causes Blood Sugar to Drop
Diabetes medication is the most common cause. Insulin and certain oral drugs can lower blood sugar too far if the dose is too high, if you skip a meal, or if you exercise more than usual. But low blood sugar can also happen in people without diabetes.
Reactive hypoglycemia causes a drop one to four hours after eating, often after a meal high in refined carbohydrates. Your body overproduces insulin in response to the sugar spike, and blood sugar crashes on the other side. This is more common in people who have had stomach surgeries, particularly gastric bypass, because food moves into the intestine faster than normal.
Hormonal deficiencies can also play a role. Problems with the adrenal glands or pituitary gland can reduce the hormones that regulate glucose production. In children, low growth hormone levels are a recognized cause. Heavy alcohol use is another trigger, because alcohol interferes with the liver’s ability to release stored glucose. Certain medications besides diabetes drugs, including quinine (used for malaria), can cause lows as well, especially in people with kidney problems.
How to Treat a Low in the Moment
The standard approach is called the 15-15 rule: eat 15 grams of fast-acting carbohydrate, then wait 15 minutes. 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 you can. If you still don’t feel better, repeat with another 15 grams.
Once your blood sugar is back above 70 mg/dL, eat a small meal or snack that includes protein and complex carbohydrates to keep it stable. A handful of crackers with peanut butter or cheese, for example, provides a slower energy source that prevents another dip.
If someone is unconscious or unable to swallow, they need emergency help. Glucagon injection kits and nasal glucagon sprays exist for this purpose, and anyone at risk for severe lows should keep one accessible and make sure the people around them know how to use it.
Low Blood Sugar During Sleep
Nocturnal hypoglycemia is particularly tricky because you can’t feel the warning signs while you’re asleep. Blood sugar below 70 mg/dL during the night often shows up as restless sleep, night sweats, nightmares, trembling, or changes in breathing. You might wake up with a headache, feeling exhausted, or with damp sheets and no clear explanation.
A bed partner may notice the signs before you do: sudden fast or slow breathing, shaking, or skin that feels hot and clammy. If nocturnal lows happen more than occasionally, a continuous glucose monitor with a low-glucose alarm can wake you before levels become dangerous. Adjusting the timing or dose of evening medications and eating a balanced bedtime snack are common strategies to prevent these episodes.
Why Frequent Lows Become Dangerous
One of the most concerning consequences of repeated low blood sugar is that your body stops warning you it’s happening. This condition, called hypoglycemia unawareness, develops because frequent episodes blunt the adrenaline response that produces those early symptoms like shakiness and sweating. The threshold at which your body sounds the alarm shifts lower and lower, so by the time you notice something is wrong, your blood sugar may already be dangerously low. People with hypoglycemia unawareness face a 25-fold or greater increase in their risk of severe episodes.
The cardiovascular effects of repeated severe lows are significant. Hypoglycemia triggers a surge of adrenaline that can cause abnormal heart rhythms, partly by driving potassium levels down in the blood. It also creates a pro-inflammatory state, promotes blood clotting, and reduces blood flow to the heart. Large clinical trials have found that people with type 2 diabetes who experience severe hypoglycemia have between 1.7 and 4.3 times the risk of death compared to those who don’t, making it one of the strongest predictors of major cardiovascular events in this population. Studies estimate a mortality risk of 2% to 4% after an episode of severe hypoglycemia in people with diabetes.
Prolonged low blood sugar can also injure the brain directly. The brain depends on a constant glucose supply, and repeated deprivation is associated with cognitive decline over time. This is separate from the temporary confusion that resolves once blood sugar comes back up. It’s cumulative damage from episodes that are too frequent, too severe, or both.
Breaking the Cycle of Unawareness
The good news about hypoglycemia unawareness is that it’s largely reversible. Strictly avoiding low blood sugar for two to three weeks can reset the body’s alarm system and restore the normal adrenaline response. This is easier said than done, especially for people on intensive insulin therapy, but it’s one of the clearest examples in medicine where a problem caused by repeated exposure can be undone by carefully preventing that exposure. Working with an endocrinologist to adjust medication targets, using a continuous glucose monitor, and being meticulous about meal timing all help rebuild awareness over time.