Low Blood Sugar: Signs, 15-15 Rule and When to Get Emergency Help
Low blood sugar, also called hypoglycaemia, generally refers to a blood glucose level below 3.9 mmol/L. Common warning signs may include sweating, shaking, hunger, dizziness, weakness or difficulty concentrating. More severe hypoglycaemia may cause confusion, seizures or loss of consciousness and requires immediate assistance. If someone becomes unconscious or has a seizure, seek emergency medical help by calling 999 in Malaysia. [1, 3, 5]
What is low blood sugar
Hypoglycaemia means blood glucose has fallen below the usual safe range. It most commonly affects people with diabetes who use insulin or certain medicines that increase insulin release. It is less common in people without diabetes and should be discussed with a healthcare professional if it occurs. [1, 3, 5]
The glucose reading is important, but symptoms can vary from person to person. Some people may notice symptoms at different glucose levels, while those who experience frequent episodes may become less aware of their usual warning signs. Follow the monitoring and action plan provided by your diabetes care team. [1, 3]
Signs and symptoms of hypoglycaemia
Symptoms of hypoglycaemia can develop quickly and may vary from person to person. Learning to recognise your usual warning signs can help you identify a possible low blood glucose episode early. [1, 2, 3]
| Early warning signs | Changes in thinking or coordination | Severe signs |
|---|---|---|
| Shaking or trembling | Difficulty concentrating | Needing another person to help |
| Sweating or clammy skin | Confusion or unusual behaviour | Seizure |
| Hunger or nausea | Blurred or changed vision | Loss of consciousness |
| Fast heartbeat or palpitations | Poor coordination | Unable to swallow safely |
| Anxiety, irritability or tingling | Drowsiness, weakness or headache | Coma |
Severe hypoglycaemia can affect a person's ability to think or function normally and may require help from another person. Seizures or loss of consciousness are emergency warning signs that require urgent medical attention. [1, 3]
Common causes of low blood sugar
Low blood sugar can happen when diabetes medicines, food intake and physical activity are out of balance. Common triggers include: [1, 3]
- Taking more insulin or diabetes medicine than needed
- Missing or delaying a meal, or eating less carbohydrate than usual
- Doing more physical activity or exercise than usual, with some effects lasting for several hours afterwards
- Drinking alcohol, especially without food
- Eating less than usual because of poor appetite or illness
- Kidney or liver problems, which can increase the risk of hypoglycaemia
- Changes in medicines, activity patterns or daily routine
Who may be at risk
- People using insulin or certain diabetes medicines, such as sulfonylureas or meglitinides
- People who have had a previous severe hypoglycaemic episode
- Older adults and people with cognitive impairment
- People with kidney or liver impairment
- People with reduced awareness of their usual low blood sugar warning signs
- People whose food intake, physical activity or alcohol intake vary considerably [1, 3, 4]
Understanding the 15-15 rule
The 15-15 rule is a commonly used approach for managing low blood glucose in a person who is conscious and able to swallow safely. [1, 3]
| Step | What the 15-15 rule involves |
|---|---|
| 1 Check | Check the blood glucose level where possible. |
| 2 Take 15 g of fast-acting carbohydrates | Examples include 150–200 mL of fruit juice or regular soft drink, 3 teaspoons of table sugar dissolved in water, or 1 tablespoon of honey. |
| 3 Wait 15 minutes | Allow 15 minutes before checking the glucose level again. Avoid activities such as driving, cycling, swimming or operating machinery while blood glucose is low. |
| 4 Check again | If the reading remains below 3.9 mmol/L, another 15 g of fast-acting carbohydrate may be taken, followed by another check after 15 minutes. |
| 5 After recovery | Once the low has resolved, have the usual meal or snack that is due at that time. |
What to do in severe hypoglycaemia
Severe hypoglycaemia can affect a person’s ability to think, respond or care for themselves. Warning signs may include marked confusion, unusual behaviour, seizures or loss of consciousness. [1, 4]
Do not leave the person alone while waiting for medical assistance. Severe or recurrent episodes should also be reviewed by the person’s healthcare team to identify possible contributing factors and help reduce the risk of future episodes. [1, 4]
What is hypoglycaemia unawareness?
Hypoglycaemia unawareness happens when the usual early warning symptoms of low blood sugar become reduced or are no longer noticed. In some cases, the first noticeable signs may be confusion or more severe symptoms. Repeated episodes of low blood sugar can make this more likely. [1]
Hypoglycaemia unawareness is associated with a higher risk of severe hypoglycaemia, so it is important to discuss any change in warning symptoms with your diabetes care team. [1]
How to reduce the risk of another low?
- Take diabetes medicines as prescribed and follow the monitoring plan provided by your healthcare team.
- Try to keep meals and physical activity as consistent as possible, and be aware that changes in routine may affect blood glucose.
- Keep a record of low blood sugar episodes, including the glucose reading, time, symptoms and possible triggers such as changes in food intake, activity or alcohol use.
- Make sure family members, friends or colleagues know how to recognise the warning signs of severe hypoglycaemia and when to seek emergency help.
- Carry medical identification if this has been recommended by your healthcare team.
- Avoid driving or operating machinery when experiencing symptoms of low blood sugar.
- If low blood sugar happens frequently, becomes more severe or your usual warning signs change, discuss this with your diabetes care team. [1, 3]
When to contact a healthcare professional
Speak with your healthcare professional or diabetes care team if low blood sugar happens frequently, occurs at night, requires help from another person, or if you notice that your usual warning symptoms have become less obvious. It is also worth discussing episodes that appear after changes in medicines, eating patterns, physical activity or health conditions that may affect blood glucose. [1, 3, 5]
If you do not have diabetes but experience symptoms suggestive of low blood sugar or have a low glucose reading, seek medical advice to understand the possible cause. [5]
Talk with a pharmacist or healthcare professional
A CARiNG pharmacist can help you understand your blood glucose readings, review factors that may contribute to low blood sugar and check that you are using your glucose meter correctly. You can explore CARiNG’s chronic disease management or find a nearby store. Pharmacist support does not replace emergency care or a medical review after severe or repeated lows.
Useful resources
Medical disclaimer: This article is for general health education and does not replace medical advice, diagnosis or treatment. The way hypoglycaemia is monitored and managed may differ between individuals depending on their health, medicines and personal circumstances.
Seek emergency medical help if a person with suspected hypoglycaemia has a seizure, loses consciousness, cannot swallow safely or does not recover as expected. In Malaysia, call 999.
Frequently asked questions about low blood sugar
What blood glucose level is considered low?
The Malaysian Clinical Practice Guidelines define hypoglycaemia as a blood glucose level below 3.9 mmol/L. Symptoms can vary between individuals, so follow the monitoring and action plan provided by your healthcare team. [1]
Can someone have low blood sugar without diabetes?
Yes, although it is uncommon. If you do not have diabetes and experience repeated symptoms suggestive of low blood sugar or have confirmed low glucose readings, seek medical advice to understand the possible cause. [5]
What if my continuous glucose monitor (CGM) says low but I feel fine?
CGMs measure glucose in the fluid between cells rather than directly in the blood, so readings may sometimes lag behind finger-prick blood glucose readings. If the CGM reading does not match how you feel, follow your device instructions and diabetes care plan; a finger-prick blood glucose test can also be used to help confirm the reading. [6]
Can low blood sugar happen during sleep?
Why is my glucose high after a low?
Blood glucose can sometimes rise after a low, particularly if more carbohydrate than needed was taken. This is why it is helpful to use the recommended amount of carbohydrate rather than taking extra “just in case.” [8]
When should repeated lows be reviewed?
Speak with your healthcare team after a severe episode, or if low blood sugar happens frequently, occurs at night, happens without the usual warning signs, or starts affecting activities such as driving or exercise. These patterns may indicate that your glucose monitoring and overall diabetes care plan should be reviewed. [1, 3]
View references 8 sources
- Ministry of Health Malaysia. Clinical Practice Guidelines: Management of Type 2 Diabetes Mellitus. 6th edition. 2020. Source
- Tan Tock Seng Hospital. Diabetes Management: Management of Low Blood Glucose (Hypoglycemia). Original source reference, accessed February 2021. Current quick guide. Source
- American Diabetes Association. Low Blood Glucose (Hypoglycemia). Accessed 5 November 2026. Source
- American Diabetes Association. Severe Hypoglycemia. Accessed 5 November 2026. Source
- NHS. Low blood sugar (hypoglycaemia). Reviewed 24 February 2023. Accessed 5 November 2026. Source
- American Diabetes Association. How to Use Your CGM for Better Diabetes Management. Accessed 5 November 2026. Source
- NHS. How and when to take short-acting insulin. Accessed 5 November 2026. Source
- American Diabetes Association. The Type 1 Diabetes Self-Care Manual. Accessed 5 November 2026. Source
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