In short
Hypoglycemia — blood glucose dropping below about 70 mg/dL — causes shakiness, sweating and confusion, and can become dangerous fast. Here's who gets it, how to treat it in minutes, and what repeated episodes are telling you.
Emergency if: Unconscious, having a seizure, or too drowsy to swallow safely — use glucagon if available and call emergency services.
On your report
Fasting Glucose, Random Blood Glucose, HbA1c, Fasting Insulin +1 more
On this page
01
What Counts as Low
Most guidelines define hypoglycemia as a blood glucose below 70 mg/dL (3.9 mmol/L), with below 54 mg/dL (3.0 mmol/L) considered clinically significant and anything causing confusion or needing another person's help classed as severe. The brain relies almost entirely on glucose, so symptoms appear quickly when supply falls.
Early symptoms are the body's adrenaline response: trembling, sweating, a pounding heart, hunger and anxiety. If the level keeps falling, the brain itself is affected — difficulty concentrating, slurred speech, blurred vision, odd behaviour, drowsiness and, in severe cases, seizures or loss of consciousness.
02
Who Gets It
By far the most common cause is diabetes treatment. Insulin and sulfonylurea tablets (such as glimepiride or gliclazide) lower glucose regardless of what you've eaten, so a skipped or delayed meal, more exercise than usual, alcohol, or a dose that no longer matches your needs can all tip you low. Metformin on its own very rarely causes hypoglycemia.
In people without diabetes it's much less common. Reactive hypoglycemia — a dip a few hours after a large, refined-carbohydrate meal — is usually mild. Rarer causes include heavy alcohol without food, adrenal insufficiency, certain medicines, severe liver or kidney disease, and, very rarely, an insulin-producing tumour.
03
Treating It: the 15-15 Rule
If you're able to swallow safely, take about 15 grams of fast-acting carbohydrate: 3–4 glucose tablets, half a cup (120 mL) of fruit juice or regular soft drink, or a tablespoon of sugar or honey. Wait 15 minutes and re-check. If you're still under 70 mg/dL, repeat. Once you're back in range, eat a snack or meal so it doesn't drop again.
Chocolate and biscuits are poor first choices — the fat slows glucose absorption. Someone who is drowsy or unconscious must not be given anything by mouth; they need glucagon (an injection or nasal spray that family members can be taught to use) or emergency care.
04
When the Warning Signs Disappear
Repeated lows blunt the adrenaline response, so some people stop noticing the early warning symptoms and go straight to confusion — a state called hypoglycemia unawareness. It's a reason to review treatment urgently, and strictly avoiding lows for a few weeks often restores the warning signs.
A very low HbA1c in someone on insulin or sulfonylureas isn't always good news: it can mean frequent unrecognised hypoglycemia, especially overnight. Continuous glucose monitoring, where available, makes these hidden dips visible.
05
Preventing the Next One
Keep fast-acting carbohydrate within reach at all times, don't skip meals after taking insulin or sulfonylureas, check before driving and don't drive if you're under 90 mg/dL (5 mmol/L), and eat something when drinking alcohol. Exercise lowers glucose for many hours afterwards, so a bedtime snack or dose adjustment may be needed on active days.
More than one or two lows a week, any severe episode, or lows without an obvious cause should prompt a treatment review — the fix is usually a small dose change, not living with the fear of it.
When to act
Emergency — act now
Unconscious, having a seizure, or too drowsy to swallow safely — use glucagon if available and call emergency services.
Same-day — call promptly
A low that needed someone else's help, a second low in the same day, or lows in someone who does not take diabetes medicines.
Routine — see a doctor
More than one or two mild lows a week, lows you no longer feel coming, or overnight sweats and headaches on waking.
Values mentioned in this story
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Sources
- Hypoglycemia — MedlinePlusmedlineplus.gov
- Low blood sugar (hypoglycaemia) — NHSnhs.uk
- Hypoglycemia (Low Blood Glucose) — American Diabetes Associationdiabetes.org
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