When your blood glucose drops below about 70 mg/dL, your body triggers an alarm response designed to push sugar back into your bloodstream. You’ll typically feel shaky, sweaty, and suddenly hungry. If levels keep falling, the effects shift from uncomfortable to dangerous, affecting your ability to think clearly and, in extreme cases, causing seizures or loss of consciousness.
Your Body’s Emergency Response
Your brain runs almost entirely on glucose. It can’t store much of its own supply, so it depends on a steady stream from your blood. The moment levels start dipping, your body launches a hormonal cascade to fix the problem fast.
Glucagon is the first responder. Released by your pancreas, it tells your liver to break down its stored sugar and dump it into your bloodstream. At the same time, your adrenal glands release adrenaline and related stress hormones, which is why low blood sugar feels so physical. If the episode drags on for hours, cortisol and growth hormone kick in as slower-acting backup, helping your body produce new glucose from non-sugar sources like protein.
This system works well in most people. But if you take insulin or certain diabetes medications, or if you have a condition that disrupts this hormonal response, the safety net can fail, and blood sugar keeps dropping.
Early Symptoms: The Adrenaline Phase
The first wave of symptoms comes from your nervous system going into overdrive. These typically appear when glucose falls into the 55 to 70 mg/dL range:
- Shaking or trembling in your hands or body
- Sweating, sometimes drenching, even in a cool room
- Fast heartbeat or pounding in your chest
- Intense hunger that comes on suddenly
- Anxiety or nervousness that seems to come from nowhere
These symptoms are unpleasant, but they serve a purpose. They’re your body’s way of telling you to eat something right now. At this stage, the problem is easy to fix.
When Your Brain Starts Running Low
If blood sugar continues to fall, a second set of symptoms appears. These come directly from your brain not getting enough fuel, and they’re more serious:
- Confusion or difficulty concentrating
- Slurred speech or unusual behavior (sometimes mistaken for being drunk)
- Blurred vision
- Weakness, dizziness, or poor coordination
- In severe cases, seizures, loss of consciousness, or coma
The behavioral changes are particularly tricky. People experiencing moderate to severe low blood sugar often don’t realize anything is wrong. They may resist help or act irritable, which is why it matters that the people around you know what hypoglycemia looks like.
How to Treat It: The 15-15 Rule
The standard approach is simple: eat 15 grams of fast-acting carbohydrate and wait 15 minutes. Then recheck your blood sugar. If it’s still below 70 mg/dL, repeat. Good options for that 15-gram dose include four glucose tablets, half a cup of juice or regular soda, or a tablespoon of honey.
The key word is “fast-acting.” A candy bar or peanut butter crackers won’t work quickly enough because fat and protein slow digestion. You want pure sugar that hits your bloodstream within minutes. Once your levels stabilize, follow up with a small meal or snack that includes protein or complex carbs to prevent another drop.
If someone is unconscious or too confused to swallow safely, do not try to put food in their mouth. This is when an emergency glucagon kit becomes critical. Glucagon is available as an injection or a nasal spray, and it signals the liver to release its stored sugar rapidly. After administering it, call for emergency help. The person’s blood sugar should be monitored every hour for three to four hours after they wake up.
Low Blood Sugar During Sleep
Nocturnal hypoglycemia is especially concerning because you can sleep right through the early warning signs. Your partner or roommate might notice restless sleep, sweating, trembling, sudden changes in breathing, or nightmares. You might wake up with a headache, feeling exhausted, or with damp sheets, and have no idea your blood sugar dropped overnight.
If nighttime lows are a recurring problem, a continuous glucose monitor can check levels every five minutes and sound an alarm when they start falling. Adjusting the timing or dose of evening medications and having a small snack before bed are other common strategies. An emergency glucagon kit should be accessible at your bedside.
When Warning Signs Disappear
One of the most dangerous complications of repeated low blood sugar is losing the ability to feel it happening. This is called hypoglycemia unawareness, and it develops gradually. Each time you experience a low episode, your body’s threshold for triggering symptoms shifts downward. If you used to feel shaky at 65 mg/dL, after repeated episodes you might not notice anything until you’re at 55 or even 50 mg/dL, by which point your thinking is already impaired.
Risk factors include having diabetes for 20 or 30 years, aggressively targeting very low glucose numbers, and conditions like dementia, anxiety, or depression that make it harder to recognize subtle body signals. If you find that your blood sugar has to drop into the 50s before you feel anything, that’s a sign this process is already underway. The good news is that carefully avoiding all lows for several weeks can partially reset your body’s alarm system.
Causes Beyond Diabetes
Diabetes medications, particularly insulin and a class of pills called sulfonylureas, are the most common cause of low blood sugar. But hypoglycemia can happen to people without diabetes too.
Reactive hypoglycemia occurs when your blood sugar drops one to four hours after eating, often because your body overproduces insulin in response to a meal. Alcohol can also trigger low blood sugar by interfering with your liver’s ability to release stored glucose. People who have had gastric bypass or other weight-loss surgery sometimes develop hypoglycemia because food moves through their digestive system much faster, causing an exaggerated insulin spike. Rare causes include insulin-producing tumors and inherited metabolic disorders.
Skipping meals, exercising more than usual, or drinking on an empty stomach can all lower blood sugar in otherwise healthy people. The episodes are usually mild and resolve on their own once you eat, but if they happen frequently, it’s worth investigating the underlying cause.
Long-Term Effects of Repeated Episodes
A single mild episode of low blood sugar, treated promptly, causes no lasting harm. But recurrent severe episodes are a different story. In the brain, repeated glucose deprivation triggers adaptive changes in how the brain uses energy and manages blood flow. Animal studies show that recurrent hypoglycemia causes metabolic changes in the hippocampus, the brain region critical for memory, and increases vulnerability to damage from reduced blood flow.
The cardiovascular effects are equally concerning. Low blood sugar promotes blood clotting and triggers inflammatory responses in blood vessel walls. These changes can persist for up to seven days after a single severe episode and contribute to the early stages of artery hardening. People with a history of severe hypoglycemia show measurable thickening of artery walls and reduced blood vessel flexibility compared to those without that history. For people already at high cardiovascular risk, a severe low can be the trigger for a heart attack or stroke.