Having low blood sugar means the glucose in your bloodstream has dropped below 70 mg/dL (3.9 mmol/L), the point where it can start affecting how you feel and function. Glucose is your body’s primary fuel, especially for your brain, and when levels fall too low, your body sends out distress signals that range from mild shakiness to confusion and, in rare cases, loss of consciousness. A reading below 54 mg/dL (3.0 mmol/L) is considered a medical urgency that needs immediate action.
How Low Blood Sugar Feels
Your body responds to dropping blood sugar in two waves. The first is an adrenaline-driven alarm system: sweating, trembling, a pounding heartbeat, sudden hunger, and a wave of anxiety. You might feel hot and clammy, notice your vision blurring, or feel unsteady on your feet. These early symptoms are your body’s way of telling you to eat something, fast.
If blood sugar keeps falling, the second wave hits your brain directly. You may struggle to think clearly, feel unusually drowsy, slur your words, or act confused. People around you often notice these changes before you do. Without treatment, this can progress to unconsciousness or seizures. The shift from “I feel a little off” to “I need help” can happen quickly, which is why recognizing the early signs matters so much.
Common Causes
In People With Diabetes
Low blood sugar is most common in people who take insulin or certain oral diabetes medications that stimulate the pancreas to produce more insulin. These medications lower blood sugar as part of their job, but they can overshoot. Skipping a meal, eating less than planned, exercising harder than usual, or drinking alcohol can all tip the balance. The combination of medication plus any of these factors is the most frequent trigger.
Among oral medications, those that directly stimulate insulin release carry the highest risk. One large population study found that people taking these drugs were about 2.5 times more likely to experience a low blood sugar episode compared to those on medications that work through other mechanisms. Higher doses and reduced kidney function increase the risk further.
In People Without Diabetes
Low blood sugar in people without diabetes is less common but does happen. The most familiar type is reactive hypoglycemia, where blood sugar dips a few hours after eating, often after a meal heavy in refined carbohydrates. The exact cause isn’t always clear, but the pattern is consistent: your body releases too much insulin in response to a meal, and blood sugar overshoots on the way down.
Other causes include heavy alcohol consumption (which interferes with the liver’s ability to release stored glucose), certain inherited metabolic conditions, rare insulin-producing tumors, and previous stomach surgeries like gastric bypass, which change how quickly food enters the small intestine.
Why Some People Stop Feeling the Warning Signs
One of the more dangerous aspects of recurring low blood sugar is that your body can gradually stop sounding the alarm. This is called hypoglycemia unawareness, and it works like a thermostat that keeps resetting lower. If your blood sugar dropped to 60 mg/dL yesterday and triggered symptoms, today you might not feel anything until it hits 55. The threshold for warning symptoms keeps sliding downward, but the threshold for losing consciousness does not. That shrinking gap between “I feel low” and “I’m unconscious” is what makes this condition so risky.
Hypoglycemia unawareness develops after repeated low episodes. It’s most common in people with type 1 diabetes and contributes to a vicious cycle: without early warning signs, lows go untreated longer, become more severe, and further blunt the body’s alarm system. Hypoglycemia-related deaths account for up to 10% of fatalities in people with type 1 diabetes.
What to Do When Blood Sugar Drops
The standard approach is called the 15-15 rule. Eat or drink 15 grams of fast-acting carbohydrates, then wait 15 minutes and recheck your blood sugar. Fifteen grams looks like four glucose tablets, half a cup of juice, or a tablespoon of honey. If your level is still below 70 mg/dL, repeat the process. Once it’s back in range, follow up with a small snack or meal to keep it stable.
If someone is too confused or drowsy to eat safely, don’t try to put food or drink in their mouth. Emergency glucagon, available as a nasal spray or injection, is the appropriate response. The nasal version is sprayed into one nostril and doesn’t need to be inhaled. If no glucagon kit is available and the person is unconscious, call emergency services immediately. Hypoglycemia is considered severe any time someone needs another person’s help to recover.
Low Blood Sugar While Sleeping
Nighttime lows are particularly tricky because you’re asleep when the warning signs appear. Clues that it’s happening include waking up drenched in sweat, having vivid nightmares, sleeping restlessly, or feeling exhausted and headachy the next morning. A bed partner might notice trembling, rapid breathing, or clammy skin.
If nighttime lows are a recurring problem, a continuous glucose monitor can check levels every five minutes and sound an alarm when they start dropping. Other practical steps include adjusting the timing or dose of evening medication and setting an early morning alarm to test blood sugar and track how often episodes occur. Keeping an emergency glucagon kit in a bedside drawer, and making sure anyone who shares your home knows how to use it, adds a critical safety net.
Long-Term Effects of Repeated Lows
A single mild episode of low blood sugar, quickly treated, causes no lasting harm. Repeated severe episodes are a different story. When the brain is starved of glucose severely enough, it can sustain real damage. Research links recurrent severe hypoglycemia to long-term cognitive problems, including difficulties with memory and concentration. In extreme and prolonged cases, chronic low blood sugar can cause mental health symptoms that resemble depression or dementia, and these don’t always fully resolve once blood sugar returns to normal.
This is why prevention matters as much as treatment. Working with your care team to identify patterns, adjusting medications, using a glucose monitor, and understanding how meals, exercise, and alcohol affect your levels are all ways to reduce the frequency and severity of lows before they accumulate into a bigger problem.