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Low blood sugar, or hypoglycaemia, is a blood glucose level that has fallen too low for the body to work normally. The NIDDK describes low blood glucose for many people with diabetes as a reading below 70 mg/dL, while the NHS uses a level below 4 mmol/L, and both note that the level treated as low can differ from person to person. A low can become serious quickly, which is why recognising it early matters.
What counts as low
The NIDDK gives a blood glucose reading below 70 mg/dL as low for many people with diabetes, and adds that individual targets can vary. The NHS describes low blood sugar as a level below 4 mmol/L.
That variation is not a contradiction. Reference ranges and personal targets differ between laboratories and testing methods, and with age, sex, pregnancy and the clinical situation, so the number that counts as low for one person is not automatically the number for another. Read the range printed on your own report, and follow the target the doctor treating you has set for you.
This page helps you recognise and respond to a low. It does not tell you what your own readings or symptoms mean. Your treating doctor interprets those.
How a low feels
The NIDDK lists mild to moderate symptoms including feeling shaky or jittery, hungry, tired, dizzy, light-headed, confused or irritable, along with heart palpitations, headaches, and problems with vision or speech. The NHS list overlaps closely and adds sweating, trembling, tingling lips, anxiety, weakness and blurred vision.
Symptoms can also appear during sleep. The NIDDK notes that blood glucose can drop while you sleep and stay low for several hours, and describes night-time signs such as crying out or having nightmares, sweating enough to make pyjamas or sheets damp, and waking up tired, irritable or confused.
Severe hypoglycaemia looks different: the person may lose consciousness or have a seizure. That is the emergency described below.
Who is at higher risk
Low blood glucose is seen most often in people taking medicines that lower blood glucose. The NIDDK names three classes: insulin, sulfonylureas, and meglitinides. If you or a family member takes any of these, ask the prescribing doctor whether they can cause low blood glucose and how to prevent and treat it. That question is exactly what the NIDDK advises asking your health care team.
Other circumstances the NIDDK describes as raising the risk include not eating enough carbohydrate or skipping meals, fasting while taking glucose-lowering medicines, being more physically active than usual, drinking alcohol without food, and being unwell. The NIDDK also states that you are more likely to develop low blood glucose if you are age 65 or older.
Never start, stop or change the dose of any medicine because of something you read here. Dose decisions belong to the doctor who prescribed the medicine.
What to do when the person is awake and can swallow
If someone is alert, able to sit up and able to swallow safely, they need fast-acting sugar straight away. The NIDDK describes the 15-15 rule: take 15 to 20 grams of glucose or carbohydrate right away, wait 15 minutes, then check the blood glucose level again. The NHS advises rechecking after 10 to 15 minutes and, if the level is still below 4 mmol/L, repeating the sugary drink or snack and checking again.
The NHS gives examples of what raises blood sugar quickly: a small glass of fruit juice or a sugary fizzy drink that is not a diet version, glucose or dextrose tablets, jelly sweets, or glucose gel. Once the level is back up and stable, the NHS advises following with a longer-acting carbohydrate.
Stay with the person while this happens. Do not leave them alone to see whether it passes, and do not wait for symptoms to get worse before acting.
Severe hypoglycaemia is an emergency
Call 108 or go to the nearest hospital immediately if a person is unresponsive or cannot be woken, is having a seizure or fit, or is so drowsy or confused that they cannot swallow safely. This is a medical emergency and needs emergency assessment, not a web page.
While waiting for help: do not put food, drink or anything else into the mouth of someone who is not fully awake — the NHS is explicit that someone who is unconscious should not be given food or drink, because they will not be able to swallow safely. Turn them onto their side into the recovery position. If the person has been prescribed an emergency treatment for severe lows and a trained family member is present, it is used exactly as the prescribing doctor instructed. Stay with them until help arrives, and tell the responding team what happened, what medicines the person takes and when they last ate.
After any severe episode the person needs to be seen, even if they recover quickly and seem completely normal again.
After a low, and lows that come without warning
Write down what happened: the time, the reading if one was taken, what the person had eaten, what activity they had done, and how long recovery took. That record is genuinely useful at the next appointment, because it helps the doctor see a pattern that no single episode shows.
Some people develop what the NIDDK calls hypoglycaemia unawareness, a condition in which you do not notice any symptoms of low blood glucose until the level has dropped very low. Lows during sleep, lows that keep repeating, and lows that arrive with no warning signs are all reasons to see the treating doctor sooner rather than waiting for a routine visit.
Wearing or carrying identification that says you have diabetes helps anyone who has to help you when you cannot explain what is happening.
Support at home
Families managing insulin routines, meal timings and monitoring at home often carry that load alone, and lows are frightening the first time they happen. Varolyn provides diabetes care at home in Bangalore and trained home nursing in Bangalore, following the plan the treating doctor has set.
A home care team supports the routine that has been prescribed. It does not diagnose, does not change medicines, and does not replace emergency services. For the wider picture of what the different glucose tests measure, see normal blood sugar levels.
Frequently asked questions
What is low blood sugar?
Low blood sugar, or hypoglycaemia, is blood glucose that has fallen too low for the body to work normally. The NIDDK describes a reading below 70 mg/dL as low for many people with diabetes, and the NHS uses below 4 mmol/L. Both note the level can differ between people, so follow the target your own doctor has set.
What are the symptoms of low blood sugar?
The NIDDK lists shakiness, hunger, tiredness, dizziness, light-headedness, confusion or irritability, palpitations, headache, and vision or speech problems. The NHS adds sweating, trembling, tingling lips, anxiety and weakness. Severe hypoglycaemia can cause loss of consciousness or a seizure, which is an emergency.
What should I do if someone with a low is awake?
If they are alert and can swallow safely, give fast-acting sugar immediately. The NIDDK 15-15 rule is 15 to 20 grams of glucose or carbohydrate, then wait 15 minutes and check again. The NHS suggests juice, a non-diet fizzy drink, glucose tablets or glucose gel, then a longer-acting carbohydrate once stable. Stay with them.
When is low blood sugar an emergency?
Call 108 or go to the nearest hospital straight away if the person is unresponsive or cannot be woken, has a seizure, or is too drowsy or confused to swallow safely. Do not put anything in the mouth of someone who is not fully awake. Turn them on their side and stay with them until help arrives.
Who is most at risk of hypoglycaemia?
The NIDDK names insulin, sulfonylureas and meglitinides as medicine classes that can cause low blood glucose, and lists skipped meals, fasting, extra physical activity, alcohol without food and illness as contributors. It also states that people aged 65 or older are more likely to develop low blood glucose. Ask your prescriber about your own medicines.
Can low blood sugar happen during sleep?
Yes. The NIDDK states that blood glucose can drop while you sleep and stay low for several hours. Signs include crying out or having nightmares, sweating enough to dampen pyjamas or sheets, and waking up tired, irritable or confused. Tell the treating doctor about any suspected night-time low.
Sources
NIDDK, NIH - Low Blood Glucose (Hypoglycemia) · NHS - Low blood sugar (hypoglycaemia) · NIDDK, NIH - Diabetes Tests and Diagnosis · MedlinePlus, NIH - Glucose tolerance test (non-pregnant)
Last checked 2 September 2026. How we write and check these pages: editorial policy.
Diabetes support and nursing at home
Varolyn provides diabetes care and trained home nursing at home in Bangalore, supporting the monitoring and routine your treating doctor has planned. A home care team does not diagnose, does not change medicines, and never replaces emergency services.