Low Blood Sugar Symptoms: Signs, Night Lows and the Rule of 15

Low blood sugar symptoms include shakiness, sweating, hunger, a fast heartbeat, irritability and confusion.^[1] In the US, low blood sugar means a reading under 70 mg/dL (3.9 mmol/L). The NHS uses below 4 mmol/L (72 mg/dL).^[4]

This guide covers the signs, what to do, the rule of 15, lows at night and low blood sugar without diabetes. This guide is general education. If you use insulin or other glucose medicines, follow the plan your diabetes team gave you.

What are the symptoms of low blood sugar?

The ADA's 2026 Standards of Care list shakiness, irritability, confusion, a fast heartbeat, sweating and hunger as typical signs.^[1] The NHS adds dizziness, tingling lips, blurred vision and feeling tired or weak.^[4] Hypoglycemia symptoms usually build as glucose falls under 70 mg/dL (3.9 mmol/L).

The ADA consumer page lists more: nausea, pale skin, clamminess, headaches, clumsiness, and nightmares or crying out during sleep.^[2] Brain-related symptoms begin below 54 mg/dL (3.0 mmol/L), which the ADA calls level 2 and says needs immediate action.^[1]

Warning signs can fade. The ADA notes that people with long-standing diabetes or repeated lows may not feel the usual symptoms.^[1] Our guide to self-monitoring glucose covers when to test.

Low blood sugar symptoms at a glance

Item.	What the evidence says.	Practical point.
Early signs.[1]	The ADA lists shakiness, irritability, confusion, a fast heartbeat, sweating and hunger.[1]	Take these as a prompt to check your glucose if you can.[1]
Other signs.[4]	The NHS adds tingling lips, blurred vision, dizziness and feeling tired or weak.[4]	Note any new pattern and tell your GP or primary care team.[4]
Signs during sleep.[2]	The ADA lists nightmares or crying out during sleep.[2]	A partner or parent may spot these before you do.[2]
Severe signs.[4]	The NHS lists a seizure or becoming unconscious.[4]	Call 999 in the UK (or 911 in the US).[4][2]

What should you do when blood sugar is low?

Raise it back up with fast carbs right away. The ADA says glucose is the preferred form for a conscious person under 70 mg/dL (3.9 mmol/L), and for most people the amount is 15 g (0.5 oz).^[1] The NHS suggests a small glass of fruit juice, 5 glucose tablets, 4 large jelly babies or 2 tubes of glucose gel.^[4]

Here is what to do when blood sugar is low and you are awake and able to swallow. Sit down, have the fast carbs, then check again after 10 to 15 minutes. The NHS says to have another sugary drink or snack if you are still below 4 mmol/L (72 mg/dL), and to check again after 10 minutes.^[4] Once your reading is back above 4 mmol/L (72 mg/dL) in the UK or 70 mg/dL (3.9 mmol/L) in the US^[2] and you feel better, the NHS advises eating something that keeps your blood sugar up for longer, such as some biscuits, a sandwich, or your next meal if it is due.^[4]

Step by step:

1. Sit down and take 15 g (0.5 oz) of fast-acting carbohydrate right away, such as glucose tablets, glucose gel or a small glass of fruit juice.^[1][4]
2. Wait 10 to 15 minutes and check your blood glucose again.^[2][4]
3. Take another 15 g (0.5 oz) of fast-acting carbohydrate if your reading is still below 4 mmol/L (72 mg/dL) in the UK or below 70 mg/dL (3.9 mmol/L) in the US.^[2][4]
4. Once your reading is back above 4 mmol/L (72 mg/dL) or 70 mg/dL (3.9 mmol/L) and you feel better, eat a longer-acting carbohydrate snack or your next meal if it is due.^[4]
5. Tell your GP or diabetes team if you use insulin or a sulfonylurea such as gliclazide or glimepiride and have repeated lows or night lows, so your plan can be reviewed.^[4][1]

Not every food works. The ADA says chocolate and peanut butter are a poor choice because the fat slows the sugar down.^[2] It also says protein may raise insulin release, so it is not the way to bring a low back up.^[1] For carb counts in everyday foods, see our guide to carbohydrates and blood sugar.

If the person is unconscious, do not give food or drink. They cannot swallow safely.^[4] Call 999 in the UK (or 911 in the US) and stay with them.

What is the rule of 15?

The rule of 15 for low blood sugar is simple. Have 15 g (0.5 oz) of fast-acting carbs, wait 15 minutes, then check again. The ADA says to have another 15 g (0.5 oz) if your reading is still under 70 mg/dL (3.9 mmol/L) or your CGM does not show it rising.^[2]

The ADA Standards of Care back the same steps and advise seeking care for ongoing lows.^[1] The NHS version uses a 10 to 15 minute wait.^[4]

If you plan a workout, our guide to exercise and glucose covers how to prepare.

Why does low blood sugar happen at night?

Hypoglycemia at night is common in some groups and often silent. In a pilot study of 25 children and teens with type 1 diabetes, CGM found night lows in 48% to 68% of them over three nights, depending on the threshold used.^[3] It was a small study.

Most of those lows went unnoticed. Of 35 night episodes picked up by CGM, 25 caused no symptoms and so finger-stick checks missed them.^[3] The ADA consumer page adds that you are less likely to wake up while asleep and your glucose is dropping.^[2]

Bedtime glucose may offer a clue. In 25 UK adults with type 1 diabetes, 12 had night lows. Their mean bedtime glucose was 7.7 mmol/L (139 mg/dL), against 11.4 mmol/L (205 mg/dL) in the 13 who had none. The authors call bedtime glucose a significant predictive factor.^[5]

Older adults are affected too. In the HYPOAGE study of 141 people aged 75 and over with insulin-treated type 2 diabetes, 92 (65.2%) spent at least 15 consecutive minutes under 54 mg/dL (3.0 mmol/L) between midnight and 6 a.m. The authors call night lows largely underdiagnosed.^[6] HYPOAGE was funded in part by Sanofi.^[6]

Night lows are a reason to talk to your clinician. The NHS lists "you've had hypos at night" among the reasons to see a GP.^[4]

Does alcohol play a part?

It can. The ADA's Section 5 recommends that people with diabetes learn the signs and self-management of delayed hypoglycemia. It also advises checking glucose after drinking alcohol, especially for those using insulin or insulin secretagogues.^[7]

Can you get low blood sugar without diabetes?

Yes, but it is rare. The NHS says it is rare to get low blood sugar without diabetes. It can sometimes be linked to malnutrition, Addison's disease or a growth (tumour) in the pancreas.^[4] If you think this is happening to you, see your GP or primary care team.

The Endocrine Society notes that insulin or insulin secretagogue use is the most common cause of hypoglycemia overall. For people without diabetes, it sets out a separate step-by-step approach.^[8] In simple terms, a clinician looks for three things: symptoms, a measured low glucose, and relief once glucose rises.

One pattern is a drop after meals. A review of this reactive hypoglycemia says it can be diagnosed when symptoms appear together with glucose under 3.3 mmol/L (about 59 mg/dL).^[9] The same review says glucose tolerance tests and mixed meals are unsuitable for diagnosis because of false results. It also links the pattern to eating habits, including alcohol.^[9] It is an older review.

Which low blood sugar symptoms need urgent help?

Any low that needs another person's help is an emergency. The ADA defines level 3 hypoglycemia as altered mental or physical functioning that requires assistance, at any glucose level.^[1] The NHS lists seizures and unconsciousness.^[4]

Low blood sugar usually means below 4 mmol/L (72 mg/dL) in the UK or below 70 mg/dL (3.9 mmol/L) in the US.^[4][2] In the UK, the NHS says to call 999 if someone may have very low blood sugar and is not responding normally or is unconscious, and a glucagon injection is not available or you do not know how to use it, or they have not recovered within 10 minutes of a glucagon injection, or they have been drinking alcohol.^[4] In the US, the ADA says to call 911 right away if someone is unconscious and glucagon is not available or no one knows how to use it.^[2]

The ADA says glucagon should be prescribed for everyone who takes insulin or is at high risk of hypoglycemia.^[1] In a trial of 75 adults with type 1 diabetes, nasal glucagon reached success at all but one visit (98.7%) compared with 100% for injection. Mean time to success was 16 minutes against 13.^[10] Two of the trial's authors worked for Locemia Solutions, the company that developed the nasal glucagon.^[10]

Here is what the labels say. The US label for BAQSIMI says the 3 mg (0.0001 oz) dose goes into one nostril, and a second dose from a new device may be given after 15 minutes if there is no response, while waiting for emergency help.^[11] The UK label for GlucaGen says adults get 1 mg (0.00004 oz) by injection and normally respond within 10 minutes.^[12] It then says to give oral carbohydrate once the person responds.

Can you drive with low blood sugar symptoms?

No, not until you have recovered. In the UK, the NHS says that if you get low blood sugar you should not drive for at least 45 minutes after your reading is back to normal. It also says to check before each journey and every 2 hours while driving.^[4]

UK law adds a duty to report. Government guidance says you must tell the DVLA if you have hypoglycaemia. You can be fined up to £1,000 (about $1,300) if you do not tell the DVLA about a medical condition that affects your driving.^[13] These are UK rules. Check local rules elsewhere.

Questions to ask your diabetes team

• Do any of my diabetes medicines, such as insulin, gliclazide or glimepiride, put me at risk of low blood sugar?^[1][4]
• Should I have a prescription for nasal or injectable glucagon, and how should my family be shown to use it?^[1][10]
• Could my bedtime glucose reading, evening exercise or alcohol explain lows during the night?^[5][7]
• What blood glucose check and waiting rules apply to me before I drive?^[4][13]

Frequently asked questions

What number counts as low blood sugar?

Under 70 mg/dL (3.9 mmol/L) in the US, and the CDC agrees.^[14] The NHS uses below 4 mmol/L (72 mg/dL). Under 54 mg/dL (3.0 mmol/L) is level 2, the point where the ADA says brain-related symptoms begin and immediate action is needed.^[1][4]

Should you give food or drink to someone who is unconscious?

No. The NHS says they cannot swallow safely.^[4] Call 999 in the UK (or 911 in the US). A person who has been prescribed glucagon may have it on hand for this situation.^[1]

Can chocolate or protein bring a low back up?

No. The ADA consumer page says chocolate and peanut butter are a poor choice, and the Standards of Care say protein may raise insulin release.^[2][1] The CDC suggests 15 g (0.5 oz) from 4 fl oz (about 120 mL, or ½ US cup) of juice or regular soda, or 1 tablespoon of sugar, honey or syrup.^[14]

Does low blood sugar always wake you at night?

No. In a pilot study of children with type 1 diabetes, 25 of 35 night lows found by CGM caused no symptoms.^[3] The CDC says you may wake up with a low but should not rely on that.^[14] Talk to your clinician if you suspect night lows.^[4][14]

Where to go next

For more on checking your numbers and discussing your targets with your care team, see:

• Self-monitoring glucose, for how and when to check your readings.
• The HbA1c test, to see what your longer-term average shows.
• Is Diabec legit?, for what is in our supplement and what it does not do.

Note: If you are pregnant, breastfeeding, or considering giving any supplement or herbal product to a child, consult your healthcare provider before making any changes to your diet, supplement routine, or prescribed medications.