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Low blood sugar (hypoglycemia): symptoms, levels and what to do
Key takeaways
- Low blood sugar (hypoglycemia) is a glucose level below 70 mg/dL (3.9 mmol/L).
- Early signs: shakiness, sweating, a fast heartbeat, hunger, irritability and dizziness.
- Treat with the 15-15 rule: 15 g of fast carbs, recheck in 15 minutes, repeat if still low.
- If someone is confused, unconscious or having a seizure, use glucagon if available and call 911.
Low blood sugar levels
| Level | Glucose | Meaning |
|---|---|---|
| Level 1 | 54–69 mg/dL (3.0–3.8 mmol/L) | Low — treat now |
| Level 2 | Below 54 mg/dL (3.0 mmol/L) | Clinically significant low — treat right away |
| Level 3 | Any value | Severe — the person needs help from someone else |
Levels from the American Diabetes Association. For normal ranges, see the blood sugar levels chart.
Hypoglycemia symptoms
- Shakiness or trembling
- Sweating, chills, clammy skin
- Fast or pounding heartbeat — adrenaline is released as glucose falls
- Hunger, nausea
- Irritability, anxiety, sudden mood change
- Dizziness, light-headedness, headache
- Blurred vision, tingling lips
- Confusion, trouble concentrating, slurred speech, clumsiness
At night, lows can cause nightmares, sweat-soaked sheets, or waking up tired or with a headache.
Some people — especially after many years of diabetes or frequent lows — stop feeling the warning signs. This is called hypoglycemia unawareness, and a continuous glucose monitor (CGM) with alerts can help.
What to do: the 15-15 rule
- Check your glucose if you can.
- Take 15 grams of fast-acting carbohydrate: 4 oz (½ cup) juice or regular soda, 1 tablespoon sugar or honey, or glucose tablets as the label directs.
- Recheck after 15 minutes. Still below 70 mg/dL? Repeat.
- Once you are back in range, eat a snack or meal if your next meal is more than an hour away.
Avoid chocolate or fatty snacks for treating a low — fat slows sugar absorption.
Severe hypoglycemia: emergency
If someone cannot safely swallow, is confused, passes out or has a seizure, do not give food or drink. Give glucagon (nasal or injection) if it is available and you know how, then call 911.
What causes low blood sugar?
- Too much insulin, or sulfonylurea medicines such as glipizide or glyburide
- Skipping or delaying a meal, or eating fewer carbs than planned
- More exercise than usual — lows can happen hours later or overnight
- Drinking alcohol, especially on an empty stomach
- Less often: kidney or liver disease, some hormone disorders, or reactive hypoglycemia a few hours after a high-carb meal in people without diabetes
Track lows to prevent the next one
Writing down each low with the time, what you ate, activity and medicine helps you and your doctor spot patterns. Cardivo lets you log glucose with context (fasting, after a meal, bedtime), sync CGM data from Apple Health, and see your heart rate alongside — a racing pulse is often the first clue. Read about the opposite problem in high blood sugar (hyperglycemia).
This guide is general wellness education based on the public sources below. It is not medical advice, diagnosis, or treatment. Cardivo is not a medical device. If you think you are having a medical emergency, call 911.
Frequently asked questions
What blood sugar level is too low?
Below 70 mg/dL (3.9 mmol/L) is low blood sugar. Below 54 mg/dL (3.0 mmol/L) is clinically significant and needs treatment right away.
What is the 15-15 rule for low blood sugar?
Eat or drink 15 grams of fast-acting carbohydrate, wait 15 minutes, and recheck. Repeat until your glucose is at least 70 mg/dL, then eat a snack or meal.
Can low blood sugar make your heart race?
Yes. As glucose falls, the body releases adrenaline, which causes a fast or pounding heartbeat, shakiness and sweating.
Sources
- American Diabetes Association — Hypoglycemia (low blood glucose)
- NIDDK — Low blood glucose (hypoglycemia)
- CDC — Low blood sugar (hypoglycemia)