Diabetes

Night-time Hypoglycaemia (Nocturnal Lows)

2025-08-30 • Updated 2025-09-14

Night-time Hypoglycaemia (Nocturnal Lows)

Night-time hypoglycaemia (low blood sugar during sleep) is common in people using insulin. It can disrupt sleep, cause morning highs (rebound), and increase fear of going low.
The goal is treat fast and prevent recurrence.

🚑 Bottom Line

• Treat immediately if < 3.9 mmol/L (70 mg/dL).
• Use 15 g fast carbs → recheck in 15 minutes.
• If unconscious or unable to swallow → glucagon + call emergency services.
• Recurrent night-time lows → review insulin regimen with your team.

Symptoms (overnight or on waking)

• Night sweats, vivid dreams, headache, restless sleep.
• Waking shaky, hungry, confused, or with a pounding heart.
• Morning high glucose (possible rebound after untreated low).

Immediate Treatment — Rule of 15

1. Take 15–20 g fast-acting carbs (glucose tabs/gel, juice).
2. Recheck in 15 minutes.
3. If still < 3.9 mmol/L (70 mg/dL), repeat step 1.
4. If the next meal is >1 hour away, add a slow carb (toast/crackers).
5. ⚠️ If unconscious or unable to swallow: a trained person should give glucagon (nasal or injection) and call emergency services.

Avoid chocolate or other high-fat foods for initial treatment — they act too slowly.

Common Causes at Night

• Excess basal insulin (too high dose or taken too late).
• Evening/late exercise increasing insulin sensitivity for hours afterwards.
• Alcohol blunting the liver’s glucose release overnight.
• Missed or very low-carb evening meal, or bolus mismatch.
• Illness or weight loss changing insulin needs.

Prevention Strategies

• Basal review: If lows occur at consistent times, discuss reducing basal dose (MDI) or set a temporary lower basal on pumps (e.g., −10% to −30%).
• Bolus timing: Avoid stacking rapid-acting insulin close to bedtime.
• Bedtime snack (when indicated): If trending down, exercised, or had alcohol, take carb + protein.
• Exercise planning: After hard evening activity, consider lower basal/bolus and snack; monitor overnight.
• Alcohol safety: Eat carbs with drinks, check before bed, and set higher alerts.
• CGM alarms: Set overnight low alerts slightly higher (4.4–5.0 mmol/L / 80–90 mg/dL); use repeat/predictive alerts.

When to Seek Medical Advice

• Two or more nocturnal lows per week, or any severe hypo needing assistance.
• Frequent morning highs after suspected overnight lows.
• New job, schedule, or medication changes affecting control.

FAQ

Is a morning high always a rebound from a low?
No — sometimes it’s the dawn phenomenon. Use CGM or a 3 a.m. finger-stick to tell the difference.

Should I always eat before bed?
No. Only if trending down, had evening exercise, or previous nocturnal lows. Unnecessary snacks can raise HbA1c.

Do automated pumps help?
Hybrid closed-loop systems can reduce nocturnal lows by adjusting basal in real time.

Further Reading

• NHS — Hypoglycaemia
• ADA — Hypoglycemia
• ISPAD Clinical Practice Consensus Guidelines — Hypoglycaemia (2022)

Related Guides

• Type 1 Diabetes — Managing Hypoglycaemia
• Diabetes Emergencies — Hypos, Highs, and Ketones
• Type 1 Diabetes — Sick-Day Management
• Managing Type 1 Diabetes During Exercise
• Insulin Types Explained

Educational only; not a substitute for professional medical advice.

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