Nocturnal hypoglycemia

The warning signs are missing. During sleep you do not feel the first signs, so a hypoglycemic episode can last for hours without being corrected [1]. Almost half of prolonged nighttime hypoglycemic episodes go unnoticed, and you only find out about them in the morning, from your sensor [1] [2].

If you sleep alone, there is also no one else to notice in time. Most severe episodes occur at night [1]. That is why sensor alarms are most justified here. With the alarms turned on, the risk of hypoglycemia drops considerably [3].

A headache on waking, unusual tiredness, clothes or sheets damp with sweat and a feeling of unrefreshing sleep. Sometimes there is also confusion on waking [1]. A fasting blood glucose below 90 mg/dL (5.0 mmol/L) in the morning can also be the sign of nighttime hypoglycemia that went unnoticed [4].

These signs are suggestive, not certain. Confirmation comes from the sensor, with the overnight graph, or from a meter reading taken during the night, sometimes by someone else. A sudden drop in the displayed value followed by an equally sudden recovery may simply be the effect of pressure on the sensor during sleep [5]. If the signs recur several mornings in a row, show your doctor the graphs for those nights.

They can be. Heavy sweating during sleep comes from activation of the sympathetic nerves, which control the sweat glands (through acetylcholine, not from adrenaline in the blood) [6] [7]. Nightmares and restless sleep are also possible signs of nighttime hypoglycemia [1].

Both also have other causes, such as fever, a room that is too warm, alcohol or stress. That is why the diagnosis is not made on these signs alone. A sensor worn for a few nights clarifies the situation far better than any guess.

Yes, but usually not for the reason many people think. The classic explanation, called the Somogyi phenomenon, assumes an exaggerated hormonal response after blood glucose falls during the night. Checking this hypothesis with sensors in real life shows that the Somogyi phenomenon is very rare [4].

Most often the cause is simpler. The nighttime hypoglycemic episode was treated with too many carbohydrates, sometimes while half awake [4]. The second explanation is the normal rise in blood glucose before waking (the dawn phenomenon) [8]. The sensor graph quickly tells these situations apart. Do not change your evening insulin dose without looking at it.

You choose the low glucose alarm threshold together with your doctor, according to your risk of hypoglycemia at night [9]. The predictive alarm warns you before the threshold is reached, so it gives you time to react [10]. A reliable nighttime alarm gets you out of hypoglycemia faster [11].

Check the volume and mode of your phone, because an alarm on silent does not help at all. If you have a child with diabetes, use remote monitoring so that the alarm also sounds in the parents' room [9].

Yes. It is one of the most predictable situations. Muscle rebuilds its glucose stores for hours after a workout and therefore becomes more sensitive to insulin. After exercise in the afternoon or evening, hypoglycemia often occurs 7–11 hours later, that is, in the second half of the night [12].

Adjustments are made in advance, not the next day. They concern the insulin dose at dinner, the overnight basal insulin and, sometimes, a bedtime snack [12]. Reducing basal insulin by about 20% after particularly strenuous exercise can prevent hypoglycemia during the following night [13]. The plan is agreed with your doctor and checked on the sensor graphs of the nights after your workouts.

The first step is the sensor, with audible alarms turned on and your phone next to the bed. The second is sharing your data with someone close to you, who can call or come over if the alarm is not turned off [10].

The third step is a serious discussion with your doctor about causes and goals. A patient who lives alone and has repeated nighttime hypoglycemia is a clear candidate for an automated insulin delivery system. The system stops insulin before blood glucose falls to a dangerous level [14]. This is not a situation to handle on your own, through caution alone.

It may be the cause, but it is not the only one. An evening basal insulin dose that is too high is recognized by a slow, steady fall in blood glucose throughout the night that appears on several nights in a row. If blood glucose starts falling in the first hours after bedtime, the cause is more often the dinner dose or a late correction, as the figure below shows [15].

The distinction is made on the sensor graph, and the doctor decides on the change. With basal insulin taken once a day, a change in the dose is felt throughout the whole day, not only at night [12].

If you use a sensor with alarms, usually not. The alarm does this job better and wakes you only when needed. Scheduled checks remain useful in special situations, such as after unusual exercise, after alcohol or after a change in your insulin dose [1].

Without a sensor, an occasional check during the night is the only way to see what is happening. Choose the higher-risk nights, not every night. If you have repeated reasons for concern, the real discussion is about access to a sensor, not about the alarm clock [10].