What are high blood sugar symptoms at night?

What people notice

Waking to urinate, usually more than once. The most common and most reliable of the group — see why this happens.

A dry mouth on waking, sometimes with a sore throat, from fluid loss overnight.

Night sweats. These are more characteristic of low blood sugar than high, which is an important distinction if you use insulin. Waking clammy, shaky and hungry points to a nocturnal hypo, not a high.

Restless legs and disturbed sleep. Both are associated with poor glucose control, though the relationship runs in both directions.

Headache on waking. Common, non-specific, and also a hallmark of sleep apnea — which is worth ruling out.

Why mornings often read high

If your fasting number is consistently higher than your bedtime number, the usual explanation is the dawn phenomenon: between roughly 3am and 8am the body releases cortisol, growth hormone and glucagon to prepare for waking, and the liver responds by releasing glucose. With enough insulin the rise is invisible. Without it, glucose climbs before you have eaten anything.

Two less common patterns produce the same morning number and need opposite responses:

• Waning insulin — glucose rises steadily from bedtime, suggesting the evening long-acting dose is not lasting
• Rebound after an overnight low — glucose drops in the small hours and the counter-regulatory response overshoots

Because the fixes are opposite, guessing is a poor strategy. A 3am reading for a few nights, or a spell with a continuous glucose monitor, will tell you which one you have.

Sleep apnea deserves a mention

Obstructive sleep apnea is strongly associated with insulin resistance and poor glucose control, and it is badly underdiagnosed. Loud snoring, witnessed pauses in breathing, waking unrefreshed and stubborn fasting numbers is a combination worth raising with a doctor — treating the apnea often improves the glucose.

When it is urgent

Waking with vomiting, deep or rapid breathing, fruity-smelling breath, or confusion alongside a high reading is not something to sleep off. Those point to diabetic ketoacidosis and need urgent care.