Can a night low happen without waking up?

Yes. The NIDDK says many people do not wake or notice symptoms, and a 2017 review found night lows are often without symptoms.

Does exercise in the evening raise the risk of a night low?

The NIDDK says physical activity can lower blood glucose for up to 24 hours afterward, so a low can come hours later, including overnight.

Can a CGM catch lows at night?

The NIDDK says a continuous glucose monitor can sound an alarm when glucose drops below the target range.

Low Blood Sugar at Night on Insulin: Signs

Q: What are the signs of low blood sugar while sleeping?

The NIDDK lists nightmares or crying out, sweating enough to dampen pajamas or sheets, and waking up tired, irritable or confused.

Short answer: Yes. The NIDDK says blood glucose can drop during sleep and stay low for several hours, often without waking the person. Signs include nightmares or crying out, sweating enough to dampen pajamas or sheets, and waking tired, irritable or confused. A 2017 review says over half of severe lows that need someone else's help happen during sleep. A continuous glucose monitor with an alarm is one tool the NIDDK names.

What a night low looks like

The NIDDK lists these signs of low blood glucose during sleep:

Crying out or having nightmares.
Sweating enough to make pajamas or sheets damp.
Feeling tired, irritable or confused after waking up.

Many people do not wake up or notice anything. The NIDDK says night lows can still interfere with sleep and affect mood and the ability to work the next day, and can make it harder to notice lows during the day.

Why they go unnoticed

A 2017 review in insulin-treated diabetes found that night lows are often without symptoms and unrecognized, and that continuous glucose monitoring shows they happen frequently. The body's alarm responses to a low are weaker during sleep, which may explain why some episodes go undetected and last longer. The authors link night lows to seizures and heart rhythm changes, and say they may lead to impaired awareness of lows; see hypoglycemia unawareness.

The Lantus label adds that its long-acting effect may delay recovery from a low (section 5.3).

What makes them more likely

The Lantus label says the risk of a low is highest when an insulin's glucose-lowering effect is at its peak, and that the timing can vary from person to person and day to day, including with the injection area. The label and the NIDDK name other triggers:

Changes in the amount, content or timing of meals, including a skipped dinner.
Extra physical activity, which the NIDDK says can lower glucose for up to 24 hours afterward.
Alcohol without enough food, which also blunts the first warning signs. See insulin and alcohol.
Being sick and eating less, and changes in other medicines or kidney and liver function.

Tools and the prescriber

The NIDDK suggests a continuous glucose monitor (CGM) for people with frequent lows or hypoglycemia unawareness, because it can sound an alarm when glucose drops below target. A low is treated with 15 to 20 grams of fast-acting carbohydrate and rechecked after 15 minutes. Glucagon is for severe lows when the person cannot treat themselves; see when glucagon is used.

The Lantus label says insulin regimen changes are made under close medical supervision, so changes to an evening dose or its timing go through the prescriber. Dose Track keeps the bedtime dose, evening exercise and drinks, and next-morning notes together, which makes a night pattern easier to see.

Read more on Dose Track: Hypoglycemia · Basal insulin · Lantus side effects · Lantus dosing schedule

General education drawn from labels, public health agencies and published studies, not personal medical advice. Your prescriber, pharmacist and the label that came with your medicine are the final word. Questions for other users? Ask in the Dose Track community.

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