Night-time Hypoglycaemia (Nocturnal Lows)

Intro

Night-time hypoglycaemia (low blood sugar during sleep) is common in people using insulin. It can disrupt sleep, raise morning glucose (rebound), and increase fear of going low. The goal is fast treatment now and pattern-based prevention.

Key Points

Treat immediately with fast carbs; recheck in 15 minutes.
Common triggers: excess evening insulin, late exercise, alcohol, missed/low-carb meals.
Prevent with dose timing/size adjustments, bedtime snacks when indicated, and CGM alerts.
Repeated nocturnal lows → review your regimen with your diabetes team.

Symptoms (may occur during sleep or on waking)

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

Immediate Treatment (Rule of 15)

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

Avoid chocolate/foods high in fat for initial treatment—they’re slower to raise glucose.

Common Causes at Night

Too much basal insulin (MDI or pump) or long-acting 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/bolus mismatch.
Recent illness or weight loss changing insulin needs.

Prevention Strategies

Basal review: If lows occur at similar times, discuss reducing basal (MDI) or set temporary lower basal on pumps overnight (e.g., −10% to −30%).
Bolus timing: Avoid stacking rapid-acting insulin close to bedtime.
Bedtime snack (when indicated): If trending down or exercised that evening, take a snack with carb + protein.
Exercise planning: Hard evening sessions? Consider lower basal/bolus and a snack; monitor more often.
Alcohol: Eat carbs with drinks; check before bed and overnight; set higher alerts.
Sick-day rules: Adjust with guidance; needs may vary.

CGM & Alarms

Set low alerts (and optional predictive alerts) slightly higher overnight (e.g., 4.4–5.0 mmol/L / 80–90 mg/dL).
Use repeat alerts and share features if available.
Review night graphs to identify patterns (time-of-night dips).

When to Seek Medical Advice

Two or more nocturnal lows per week, or any severe episode needing help.
Frequent morning highs after suspected overnight lows.
New job/schedule, medication, or health change affecting control.

FAQ

Is the morning high always a rebound from a low?
Not always—could be the dawn phenomenon. Check a CGM trace or set an alarm for a 3 a.m. finger-stick to distinguish.

Should I always eat before bed?
Only if indicated (downward trend, recent exercise, or previous nocturnal lows). Unnecessary snacks can raise A1C.

Are automated pump systems helpful?
Hybrid closed-loop systems can reduce nocturnal lows by adjusting basal in real time; discuss options with your team.