Nocturnal hypoglycemia refers to low blood sugar levels at night in a person who has diabetes. Blood sugar levels can drop below their target range at night if a person eats too little food after taking his or her usual nighttime insulin dose or takes more insulin than prescribed in the evening.

Low blood sugar can also happen when:

• There are problems with the insulin (for example, it is expired or it has not been stored properly).
• The amount of insulin changes (for example, if the person is working with the doctor to adjust the dose).
• The person with diabetes is sick.

But sometimes the reason is not obvious. Nocturnal hypoglycemia may also be related to previous exercise or increased physical activity.

Signs of low blood sugar at night include:

• Restlessness, unusual noises, talking, or nightmares.
• Waking up feeling tired or having a headache.
• Having damp clothing and bed linens in the morning (night sweats).
• Having a high blood sugar level in the morning.

Testing blood sugar levels at about 2 a.m. to 3 a.m. for a few consecutive nights may help a person find out whether low blood sugar is causing the symptoms. Continuous glucose monitoring (CGM) devices can also help. Some of these devices sound an alarm when blood sugar is too high or too low.

Nocturnal hypoglycemia may be prevented by decreasing the evening insulin dose or by adding more food to the bedtime snack.