Sneaky signs of high and low blood sugar — and what to do about them

Glucose (blood sugar) is the fuel that keeps our bodies running. Your blood sugar level changes all the time. It can go too high or too low as part of everyday life. 

“While we are sleeping, our glucose levels may be lower,” explains Chris Memering, M.S.N., R.N., a spokesperson for the Association of Diabetes Care and Education Specialists. “If we get chased by a bear while on a walk in the woods, our glucose levels are going to rise and then drop after using all that energy to run away.” 

• Blood sugar that’s too high is called hyperglycemia. If it stays high, you develop diabetes. And that can cause other health problems. Heart disease, kidney disease, and vision loss can all be related to diabetes. 

• Low blood sugar is called hypoglycemia. It can cause mild symptoms or serious ones, like seizures. 

Blood sugar spikes or dips are more common in people with prediabetes and diabetes. But the signs can be easy to miss. 

“I wish the signs were something like breaking out in purple polka dots,” admits Memering. “They can be slow and sneaky.” 

It's important to understand how to spot high and low blood sugar. This is especially true if you have prediabetes or type 2 diabetes.  

What causes blood sugar to rise? 

A lot of things may cause your blood sugar to rise when you have diabetes or prediabetes: 

• Processed foods (especially simple carbs) and alcohol 
• Caffeine 
• Stress 
• Infections or illness 
• Lack of exercise 
• Dehydration 
• Hormone changes 

A bad night’s sleep or a very late dinner can also influence your blood sugar levels. So can taking medications for your allergies. 

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What are the warning signs of high blood sugar? 

If you have not been diagnosed with diabetes, your body will send you different clues that something might be wrong.  

Diabetes educator Chis Memering recommends asking yourself a few questions: 

• Are you thirsty all the time? 
• Do you have to pee often, especially at night? 
• Are you feeling hungry? 
• Have you been losing weight (without trying)? 
• Do you lack energy? 
• Do you have a dry mouth? 
• Are you having trouble focusing? 

If you answer yes to one or more, call your doctor and ask if you should get tested for diabetes. 

What are the sneaky signs of high blood sugar?  

You should also be on the lookout for these lesser-known red flags: 

Wounds that don’t heal quickly. High blood sugar narrows your blood vessels. Less blood flow slows down healing. 

High blood sugar can also affect your immune system, making you more likely to get an infection. 

Your vision is blurry. With high blood sugar, your blood vessels can begin to leak. Fluid then builds up in the retina. This condition is called diabetic retinopathy. 

The retina is the part of the eye that takes in images and sends them to the brain. Extra fluid there affects the pressure in the eyes. It can cause you to lose your eyesight. 

“For some, these signs don’t happen until blood sugar values get really high,” says Memering. Annual eye exams may be the only chance to find it. 

What causes blood sugar to drop? 

If you have diabetes, your blood sugar levels may fall when you: 

• Skip or delay meals 
• Exercise  
• Take too much diabetes medicine 
• Have other reactions because of your medications 
• Drink alcohol 

What are the warning signs of low blood sugar? 

According to Memering, common signs of low blood sugar include when you: 

• Have a fast heart rate 
• Sweat or feel cold and clammy 
• Feel weak or tired 
• Are dizzy or lightheaded  
• Tremble or shake 

What are the sneaky signs of low blood sugar? 

There are some surprising signs too: 

You have headaches. You might even wake up with a headache. “That could mean your blood sugar dropped while you slept,” says Memering. 

Your vision is blurry. This is also a sign of low blood sugar. 

Your mood changes. You may be cranky, confused, or sad. Blood sugar powers your brain so low blood sugar affects it too. 

“Sometimes, people have very individual symptoms of hypoglycemia, such as visual auras or tingling lips,” says Memering. 

If you have diabetes, you need to check your blood sugar level to know how low it has fallen.  

“This is my one hard and fast rule. Check with any sign or symptom of low blood sugar,” says Memering. It’s important to deal with hypoglycemia before it gets worse. 

Treating high or low blood sugar  

To stabilize high blood sugar, Memering suggests trying the following: 

• Drink lots of water or other non-sugary beverages. 
• Go for a walk or do something physical.   
• Lower your stress level. Try meditation or journaling. Vent to a willing friend. 

Look for a pattern in your spikes with your care team. Together you might notice a behavior that you can change. If your diabetes has changed, your plan needs to as well.  

“For low blood sugar, you need to raise it quickly,” says Memering. Below 70 mg/dL is of concern.  

Follow the 15-15 rule, she says. 

• Eat something with 15 grams of carbohydrates. Make a choice that will convert into glucose quickly. Memering suggests 4 ounces of regular juice or milk, a tablespoon of honey, four tablets of glucose, or a tube of glucose gel. 

• Wait 15 minutes and check your blood sugar. “Still low? Repeat the treatment and check again,” she says. 

“With low blood sugar, you want a fast-acting source of sugar. But skip chocolate or peanut butter,” says Memering. The fat delays the body’s ability to absorb sugar. 

“If you have low blood sugar regularly, get a prescription for glucagon,” she says. This comes as a shot or a nasal spray.  

Being in tune with your body will help you start to see any signs of high or low blood sugar. What lets you know for sure is checking your blood sugar levels. Your doctor can order a blood lab test to check your hemoglobin A1C or a Glucose Management Indicator (GMI). 

If you have prediabetes, get your levels checked at least once a year. 

If you have diabetes, your doctor will tell you how often you should check your blood sugar yourself. 

Sources: 

Blood Glucose (Blood Sugar) MedlinePlus, National Library of Medicine.  
Blood Glucose and Insulin at Work American Diabetes Association. 
Sleep and Blood Glucose Levels Sleep Foundation. 
Seasonal Allergies and Diabetes Associations of Diabetes Care & Education Specialists 
Hyperglycemia (High Blood Sugar) American Diabetes Association. 
Hyperglycemia in Diabetes Mayo Clinic. 
Diabetes American Academy of Family Physicians. 
Diabetes and Vision Loss Centers for Disease Control and Prevention.  
Low Blood Sugar (Hypoglycemia) Centers for Disease Control and Prevention. 
How to Treat Low Blood Sugar (Hypoglycemia) Centers for Disease Control and Prevention. 
Glucagon & Other Emergency Glucose Products American Diabetes Association.  

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