High Blood Sugar Warning Signs

While chronic high blood sugar is the hallmark of diabetes, a prolonged spike can happen in anyone and should be checked out as soon as possible to prevent serious complications. Chitra Reddy, MD, UnityPoint Health endocrinologist, shares high blood sugar symptoms and risks and what to do if you suspect your levels are too elevated.

What Causes High Blood Sugar

Hyperglycemia, or high blood sugar, occurs when there’s too much sugar in your blood, because your body either doesn't have enough insulin or can't use it properly. Insulin is a hormone, made by the pancreas, that helps your body use sugar (glucose) from food for energy or storage.

What Causes High Blood Sugar Without Diabetes?

If you don't have diabetes, high blood sugar can be triggered by several factors:

• Hormonal Changes: Conditions like thyroid disorders or pregnancy — placenta hormones can cause insulin resistance.
• Illness or Infection: Your body puts out excess cortisol to fight infection. For instance, an illness like the flu can raise your blood sugar.
• Medications: Steroids, antipsychotic prescriptions, diuretics (water pills), statins for high cholesterol, beta-blockers, certain hormonal treatments and some over-the-counter decongestants can sometimes cause blood sugar pikes.
• Stress: Chronic stress causes the body to release cortisol, which raises blood sugar.
• Sugary Drinks: Sugary cocktails and other drinks high in refined sugar and low in fiber can cause blood sugar to spike quickly. Dr. Reddy says, "These spikes are too fast for the pancreas to handle, especially if you're predisposed to insulin resistance."
• Trauma or major surgery: This causes the body to release high levels of stress hormones (like cortisol and adrenaline), which trigger the liver to produce extra sugar for a potential "fight or flight" response, raising blood sugar.

What is Considered a High Blood Sugar Level?

Understanding your blood sugar range is the first step in recognizing a potential problem.

• More than 126 mg/dL: Indicates diabetes or prediabetes
• More than 250-300 mg/dL: Symptoms become more pronounced
• 300-400 mg/dL: This is an emergency, contact your doctor immediately
• More than 600 mg/dL: Severe, life-threatening risk of complication known as diabetic ketoacidosis (DKA)

Dr. Reddy notes that dangerously high levels don't typically happen overnight.

"Blood sugar usually builds up gradually. When levels exceed 600 mg/dL, the body is no longer able to process the amount of sugar, and patients risk severe dehydration,” she says.

What Does High Blood Sugar Feel Like?

Acute high blood sugar symptoms are similar for most adults and don’t significantly differ between men and women, though women may notice more yeast infections long-term.

When you have too much sugar in one day, especially if you have prediabetes or undiagnosed diabetes, you may experience the following:

• Blurred vision
• Confusion or altered mental status
• Dehydration
• Dry mouth
• Excessive thirst
• Fatigue
• Frequent urination
• Nausea or vomiting

For non-diabetics who’ve consumed a high amount of sugar, symptoms may simply include increased sugar cravings and fatigue.

Does High Blood Sugar Make You Sleepy?

"Yes, it's like a 'food coma,' as your energy is focused on processing the overload," Dr. Reddy says.

When blood sugar is very high, the body's cells can't properly access the glucose they need for fuel. Instead, the body shifts energy toward the complex, resource-intensive job of trying to process the excess sugar and correct the chemical imbalance, leaving you feeling fatigued and lethargic — much like the heavy tiredness experienced after a large meal.

Can High Blood Sugar Cause Dizziness or Headaches?

While severe high blood sugar can cause dizziness or a headache, they’re more common when high blood sugar dips quickly after a spike.

High Blood Sugar in the Morning

Many people, especially those with diabetes, experience high blood sugar levels in the morning due to the Dawn Phenomenon. This is when the body releases hormones (like cortisol) while waking up, causing the liver to make glucose overnight. For non-diabetics, the body releases enough insulin to manage this increase, but for those with diabetes, the body can’t compensate.

How to Lower High Blood Sugar Quickly

Immediate action focuses on halting the rise and safely managing the glucose overload. However, many people try quick fixes that don't actually work.

"You can’t really 'detox' or flush sugar out of your system entirely," Dr. Reddy says. "Insulin is the only way to reduce blood sugar immediately."

However, if your blood sugar is high (upper 100s to 300 mg/dL), here’s what to do to prevent further spikes:

• Contact your provider: If your blood sugar is 250–300 mg/dL or higher, call your doctor. They may need to adjust your medication or insulin.
• Destress: Turn to relaxation and stress-reducing techniques. Chronic stress elevates cortisol.
• Drink water: High blood sugar often leads to dehydration. Drinking lots of water helps reduce concentrated blood sugar levels. (When patients arrive at the hospital with severe hyperglycemia, IV fluids are given immediately.)
• Exercise: Regular physical activity helps your body use glucose more efficiently.
• Get quality sleep: Good sleep is essential for hormone balance and blood sugar regulation.

Sugar Detox Timeline

While a short-term "sugar detox" may temporarily lower blood sugar, Dr. Reddy advises against extreme crash diets.

"Reducing or cutting out added sugar is effective, but short-term detoxes don't address the psychological aspects and root causes of high blood sugar,” she says.

Temporary detoxes fail because they don't fix underlying mental habits, like:

• Cravings and addiction: The powerful desire or dependency the brain develops for sweets.
• Emotional eating: Using sugar to cope with stress, sadness, boredom or anxiety.
• Habit and routine: Eating sweets out of routine or convenience, often without realizing it.

“Sustainable lifestyle changes are always the better path,” Dr. Reddy adds.

When to See a Doctor About High Blood Sugar Symptoms

If you have severe or concerning high blood sugar warning signs, or if your at-home reading is consistently over 250 mg/dL, contact your healthcare provider right away.

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