Low blood sugar, or hypoglycemia, happens when glucose levels drop below what your brain and body need to function normally, generally under 70 mg/dL. It comes on quickly, often within minutes, and produces a recognizable set of warning signs: shakiness, sweating, a racing heart, and sudden hunger. Catching these signs early and treating them right away is the key to preventing a more dangerous drop that can affect thinking, coordination, and in severe cases, consciousness.

Early Warning Signs

When blood sugar starts to fall, the body releases adrenaline and other stress hormones to push glucose back up. This is what produces the classic early symptoms, and they usually appear fast:

• Shakiness or trembling, especially in the hands
• Sweating, often described as sudden and cold, even in a cool room
• A fast or pounding heartbeat
• Sudden, intense hunger
• Dizziness or lightheadedness
• Irritability, anxiety, or a sudden mood change
• Tingling or numbness around the lips or fingers
• Pale skin
• Headache

These early signs are the body's alarm system. If you catch them and treat the low right away, most episodes resolve within 15 to 20 minutes without escalating further.

Signs of a Worsening or Severe Low

If blood sugar keeps dropping, or the early signs go unnoticed or untreated, symptoms shift from physical discomfort to changes in brain function, glucose is the brain's primary fuel source, so a serious drop affects thinking and behavior:

• Confusion or trouble concentrating
• Slurred speech
• Blurred or double vision
• Clumsiness or poor coordination, which can look like intoxication to bystanders
• Unusual behavior, such as acting confused about time or place
• Extreme fatigue or weakness
• Seizures
• Loss of consciousness

This second tier of symptoms is a medical emergency. A person experiencing confusion, a seizure, or loss of consciousness from low blood sugar cannot safely treat themselves and needs help from someone else right away.

What Causes Blood Sugar to Drop Too Low

Hypoglycemia is most common in people being treated for diabetes, but it has several possible causes:

Diabetes Medication

Insulin and sulfonylurea medications (such as glipizide or glyburide) lower blood sugar and can cause it to drop too far if the dose is too high relative to food intake, activity, or timing.

Skipped or Delayed Meals

Taking diabetes medication and then skipping, delaying, or eating a smaller meal than usual is one of the most common causes of an unexpected low.

Increased Physical Activity

Exercise increases glucose uptake by muscles, sometimes for many hours afterward, which can cause lows well after a workout is finished, not just during it.

Alcohol

Alcohol suppresses the liver's ability to release stored glucose. Drinking, especially without food, can cause delayed low blood sugar, sometimes hours later or even the next morning.

Other Causes

Less commonly, hypoglycemia can occur without diabetes medication, related to certain other medications, heavy alcohol use, hormone deficiencies, some post-bariatric surgery patients, or rare insulin-producing tumors. Reactive hypoglycemia, a drop a few hours after eating, is another pattern some people experience.

When to Seek Medical Care

How to Treat a Low Right Away

The American Diabetes Association recommends the "15-15 rule" for mild to moderate lows in someone who is awake and able to swallow safely:

1. Eat or drink 15 grams of fast-acting carbohydrate, such as glucose tablets, half a cup of regular (not diet) soda or juice, or a tablespoon of sugar or honey.
2. Wait 15 minutes, then recheck blood sugar if a meter is available.
3. If it is still below 70 mg/dL, repeat with another 15 grams of fast-acting carbohydrate.
4. Once blood sugar is back in a normal range, eat a small snack or your next meal to help keep it stable.

For someone who is unconscious, having a seizure, or unable to swallow safely, do not give food or liquid by mouth. If glucagon (an injection or nasal spray prescribed for severe lows) is available, use it and call 911.

Reducing the Risk of Future Lows

• Check blood sugar as recommended by your care team, especially before driving, exercising, or bed
• Never skip meals if you take insulin or a sulfonylurea
• Carry a fast-acting carbohydrate source at all times if you are prone to lows
• Wear a medical alert bracelet or ID if you have frequent or severe hypoglycemia
• Talk to your care team about whether a continuous glucose monitor could help catch drops earlier
• Ask your care team about glucagon if you have severe lows, and make sure someone close to you knows how to use it