Low blood sugar, called hypoglycemia, typically announces itself through a predictable set of warning signs: shakiness, sweating, sudden hunger, and a racing heart. These symptoms usually start when blood sugar drops below 70 mg/dL. But the signs shift as levels fall further, and some people lose the ability to feel them at all. Knowing what to look for, and when to grab a meter, can help you catch a low before it becomes dangerous.
The First Warning Signs
Your body’s earliest response to dropping blood sugar is an adrenaline surge. This produces symptoms that feel physical and urgent: shaking hands, sweating (especially cold or clammy skin), a pounding or fast heartbeat, sudden intense hunger, and anxiety that seems to come out of nowhere. These signs tend to appear when blood sugar dips into the 60s or low 70s, and they’re your body’s way of telling you to eat something now.
If blood sugar keeps falling, a second wave of symptoms kicks in. These are caused by your brain not getting enough fuel, and they feel very different. You may notice difficulty concentrating, confusion, blurred vision, dizziness, weakness, or unusual fatigue. Some people act strangely or seem drunk, slurring words or behaving erratically, without realizing anything is wrong. This shift from “shaky and hungry” to “confused and uncoordinated” is the key signal that a low is getting serious.
Lows That Happen at Night
Blood sugar can drop while you sleep, and you won’t be awake to notice the usual warning signs. Nocturnal hypoglycemia is more likely if you skipped dinner, exercised in the evening, drank alcohol before bed, or take certain types of insulin that peak overnight.
Clues that it happened include waking up drenched in sweat, having vivid nightmares, or feeling unusually groggy and headachy in the morning. A partner might notice restless sleep, trembling, sudden changes in your breathing pattern, or hot and clammy skin. If you suspect nighttime lows, checking your blood sugar before bed and again when you wake up can help confirm the pattern.
When You Stop Feeling the Symptoms
Some people, particularly those on insulin or certain diabetes medications, lose the ability to sense low blood sugar over time. This is called hypoglycemia unawareness, and it develops through a frustrating cycle: repeated lows train your body to delay its alarm signals. Each episode pushes the threshold lower. If yesterday you felt symptoms at 60 mg/dL, today you might not notice anything until you hit 55. The problem is that the blood sugar level triggering unconsciousness doesn’t shift down with it, so the gap between “I feel fine” and “I’ve passed out” keeps shrinking.
A telling sign is if you only notice lows when your blood sugar is already in the 50s or below. If that sounds familiar, you’re at higher risk for severe episodes and should talk to your care team about adjusting your targets or monitoring more frequently.
The Only Way to Know for Sure
Symptoms are useful clues, but a blood sugar reading is the only reliable confirmation. A standard finger-prick glucometer measures glucose directly from capillary blood and reflects close to real-time levels. If you get a reading below 70 mg/dL while feeling symptomatic, that’s your answer.
Continuous glucose monitors (CGMs) are convenient but come with a lag. Because they measure glucose in the fluid surrounding your cells rather than in your blood directly, readings can trail behind actual blood sugar by 5 to 20 minutes. During a rapid drop, like after exercise, this delay matters. Your CGM might display 70 mg/dL while your actual blood sugar is already at 55. The trend arrows on your device help bridge this gap: a single downward arrow means levels are falling steadily, and double downward arrows mean they’re plummeting. If you see downward arrows and feel symptomatic, treat the low rather than waiting for the number to catch up.
Feeling Low When You’re Not Actually Low
It’s possible to feel every classic symptom of low blood sugar, shaky, sweaty, mentally foggy, while your actual reading is perfectly normal. This is called pseudohypoglycemia, defined as hypoglycemia-like symptoms with a measured blood sugar above 70 mg/dL. It’s especially common in people whose blood sugar has been running high for a while. When your body adjusts to levels of 200 or 250, a sudden drop to 120 can feel like a crash even though 120 is a healthy number.
This is one more reason a meter matters. If you’re treating “lows” based only on how you feel, you may be eating extra carbs your body doesn’t need. A quick finger stick tells you whether to treat or wait it out.
What Causes Blood Sugar to Drop
For people with diabetes, the most common triggers are too much insulin, delayed or skipped meals, and unexpected physical activity. Alcohol also lowers blood sugar, sometimes hours after your last drink, which is why evening drinking is a setup for overnight lows.
Low blood sugar in people without diabetes is less common but does happen. Reactive hypoglycemia causes a dip one to four hours after eating, often after high-carb meals. It’s more frequent in people who’ve had stomach or gastric bypass surgery, which changes how quickly food moves through the digestive system. Accidentally taking someone else’s diabetes medication is another cause. In rare cases, underlying conditions affecting the liver, kidneys, or hormone-producing glands can trigger fasting hypoglycemia.
How to Treat a Low Quickly
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 recheck your blood sugar. If it’s still below 70 mg/dL, repeat. Keep repeating until you’re back in your target range. Young children, especially toddlers and infants, typically need less than 15 grams per round.
Good options for those 15 grams include four glucose tablets, a small tube of glucose gel, four ounces of juice or regular soda, or a tablespoon of honey. Avoid foods with fat or protein mixed in (like chocolate or peanut butter crackers) as a first treatment, because fat slows digestion and delays the sugar from reaching your bloodstream.
Signs of a Severe Low
When blood sugar drops far enough, a person may become unable to help themselves. Severe hypoglycemia looks like seizures, loss of consciousness, extreme confusion, or an inability to swallow safely. At this point, do not try to put food or liquid in the person’s mouth, as they could choke. This is when injectable or nasal glucagon is used: it triggers the liver to release stored sugar into the bloodstream and can be given even while someone is unconscious. If glucagon isn’t available or the person doesn’t recover within a few minutes, call emergency services.
If you’re on insulin or medications that carry a risk of lows, keeping a glucagon kit accessible and making sure the people around you know how to use it can be the difference between a scary moment and a medical emergency.