Blood sugar dropping at night typically causes heavy sweating, damp sheets, a racing heart, restless sleep with nightmares, and a morning headache that will not lift. Many people also wake up with a paradoxically high blood sugar in the morning (the Somogyi rebound effect). Nocturnal hypoglycemia is most common in people taking insulin or sulfonylureas, and it is one of the most important things to detect because it can progress to seizure or unresponsiveness if untreated.
Why Blood Sugar Drops at Night
Overnight the body normally relies on steady liver glucose output to maintain blood sugar while you sleep. Hypoglycemia develops when insulin or other glucose-lowering medication exceeds the body’s overnight needs. Common triggers:
- Too much basal (long-acting) insulin or a mistimed bedtime dose
- Sulfonylureas (glipizide, glyburide, glimepiride) without enough carbs at the last meal
- A late-afternoon or evening workout that depleted muscle glycogen
- A skipped or delayed dinner
- Alcohol with or after dinner — the liver stops releasing glucose while it clears ethanol
- Weight loss or a new exercise routine that increased insulin sensitivity
- Kidney dysfunction reducing insulin clearance
- Gastroparesis delaying food absorption from a normal dinner
Symptoms You Will Actually Notice
Because you are asleep, many of the usual low-blood-sugar warning signs pass unnoticed. What wakes you up, or what you notice in the morning, is usually the tail end of the reaction.
| Stage | Typical Signs |
|---|---|
| While it is happening | Heavy sweating, damp pajamas or sheets; racing or pounding heart; restless movements or kicking; nightmares or vivid dreams; crying out in sleep; tremor; cold or clammy skin |
| On waking | Persistent headache; feeling exhausted despite hours of sleep; foggy or irritable mood; nausea; blurry vision |
| Morning glucose | Unexpectedly high reading — the Somogyi or counterregulatory rebound from the low hours earlier |
| Severe / emergency | Confusion, inability to follow commands, seizure, unresponsiveness — a 911 situation |
Confirming an Overnight Low
The clearest evidence is a continuous glucose monitor trace showing a dip below 70 mg/dL (3.9 mmol/L) overnight. Without a CGM, indirect clues help:
- Check your glucose as soon as you wake, before eating or dosing.
- If you wake in the middle of the night feeling off, check right away.
- Keep a sleep and symptom log for 2 to 4 weeks.
- Ask your doctor about ordering a CGM or a trial of a professional flash glucose monitor.
If you are taking insulin or sulfonylureas and do not yet use a CGM, it is reasonable to ask whether one is indicated. Many insurance plans now cover CGMs for people on intensive insulin therapy.
Treating an Overnight Low (Rule of 15)
If you wake up and your glucose is under 70 mg/dL (3.9 mmol/L):
- Consume 15 grams of fast-acting carbohydrate — 4 ounces (120 mL) of juice or regular soda, 3 to 4 glucose tablets, 1 tablespoon of honey, or a glucose gel packet.
- Wait 15 minutes, then recheck.
- If still under 70 mg/dL, repeat with another 15 grams.
- Once back above 70 mg/dL and at least an hour from your next meal, have a small protein-plus-carb snack (e.g., crackers with cheese) to prevent another dip.
- Note the episode, the time, and what you did in the hours before so you can discuss it with your care team.
When It Is an Emergency
Severe hypoglycemia — someone cannot be roused, is confused or combative, or has a seizure — is a medical emergency. Household members should:
- Call 911.
- Give glucagon by injection (Gvoke, Zegalogue) or nasal spray (Baqsimi) if available — it raises glucose within 10 to 15 minutes.
- Place the person on their side to protect the airway.
- Do not try to force food or drink into an unconscious person — aspiration risk.
Every person on insulin or sulfonylureas should have an unexpired glucagon kit at home and at least one other person trained to use it.
Preventing Overnight Lows
- Set CGM low-glucose alerts at 80 or 85 mg/dL at bedtime to catch drops early.
- Do not skip dinner, especially on insulin or sulfonylureas.
- Reduce bedtime basal insulin after heavy afternoon or evening exercise — ask your doctor for a rule of thumb you can apply.
- Avoid alcohol on an empty stomach, especially close to bedtime.
- Check glucose at bedtime; if it is under 100 mg/dL on insulin, have a complex-carb snack.
- Review dose timing for long-acting insulin; glargine and degludec behave differently across 24 hours.
- Ask about an insulin pump or hybrid closed-loop system if you have recurrent overnight lows. These systems reduce basal insulin automatically when glucose is trending low.
When to Call Your Doctor
Contact your diabetes team promptly if you have:
- More than one overnight low per week
- Any low below 54 mg/dL (Level 2 hypoglycemia)
- Loss of hypoglycemia symptoms while still experiencing lows (hypoglycemia unawareness)
- An episode that required another person’s help
- Any seizure or emergency glucagon use
These patterns nearly always mean medication doses need adjustment. For overall management strategy, see our treatment hub, and for broader symptoms of blood sugar problems.
The Bottom Line
If you wake up sweaty, headachy, and exhausted, with damp pajamas or a racing heart, your blood sugar may have dropped while you slept. Nocturnal hypoglycemia is serious, common in people taking insulin or sulfonylureas, and highly preventable once it is detected. Ask your care team about a CGM with low-glucose alarms, know how to use the Rule of 15, keep glucagon on hand, and review any overnight low at your next appointment so the underlying cause can be fixed.
