How to Spot Low Blood Sugar & Nighttime Lows Early with CGM Alerts

Why are nighttime lows easy to miss?

A nighttime (nocturnal) low is a hypo that happens overnight, while you are asleep. The threshold is the same as during the day — below 70 mg/dL (3.9 mmol/L), or below 4 mmol/L as Diabetes UK describes it — but because you are asleep you may not notice the usual warning signs.

In studies of people with type 1 diabetes, a large proportion of severe hypoglycaemia — around half — occurs overnight, and many nighttime lows are not felt. In the DCCT, roughly 55% of severe episodes happened at night. These figures come from type 1 diabetes research and describe groups of people studied, not any one individual.

This is one reason a CGM can help: the American Diabetes Association notes that CGM can reveal asymptomatic hypoglycaemia — lows you did not feel — and help you and your care team identify overnight patterns.

How do you set up low-glucose alerts?

On many CGMs alerts are optional and must be switched on. General steps for setting up low-glucose alerts:

• •Agree a low threshold with your doctor or diabetes team — for example a level around 70 mg/dL (3.9 mmol/L) or 4 mmol/L — based on your treatment plan.
• •Turn the low alert on in your CGM app; on many systems alerts are off by default.
• •Keep alerts enabled overnight so you can be notified of a nighttime low while you sleep.
• •Check your phone's volume, “do not disturb” and notification settings so an overnight alert can actually wake you.
• •Review your overnight readings and patterns with your care team, and adjust your settings on their advice.

When should you get medical advice?

Set your thresholds and alert settings with your doctor or diabetes care team, and follow the plan you agree for what to do when you get a low alert.

Because a CGM measures glucose in the fluid just under your skin rather than in blood, its reading can lag your blood glucose by around 5–15 minutes. Clinical guidance — for example from the NHS — advises doing a finger-prick blood glucose check before treating a suspected low or making a treatment decision.

NICE guidance (NG17) says adults with type 1 diabetes should be offered a choice of real-time or flash CGM, and lists the fear, frequency, awareness and severity of hypoglycaemia among the factors to consider. This is guidance for clinicians, not a product claim.

The Vixxa 2 is indicated for adults (18 years and older) and is licensed for import in India under the Medical Device Rules 2017 (CDSCO import licence IMP/MD/2025/000209). A CGM is a monitoring aid, not a treatment. It does not prevent or treat low blood sugar. If you experience low blood sugar, follow your doctor's advice and treatment plan. Individual results vary, and this page is not a substitute for medical advice.