High and Low Blood Sugar Symptoms

High and low blood sugar symptoms can feel very different, but some warning signs overlap. High blood sugar often causes increased thirst, frequent urination, fatigue and blurred vision, while low blood sugar is more likely to cause shakiness, sweating, hunger, dizziness and confusion.

Because symptoms alone cannot always tell you whether your blood sugar is high or low, checking your glucose with a blood glucose meter or continuous glucose monitor (CGM) is the most reliable way to know.

Quick Answer: What Are the Symptoms of High and Low Blood Sugar?

High vs. Low Blood Sugar Symptoms at a Glance

Symptom	High Blood Sugar	Low Blood Sugar
Increased thirst	Common	Less common
Frequent urination	Common	No
Shakiness	Less typical	Common
Sweating	Less typical	Common
Hunger	Can occur	Common
Fatigue or weakness	Common	Common
Blurred vision	Can occur	Can occur
Headache	Can occur	Can occur
Dizziness	Can occur	Common
Irritability	Less typical	Common
Confusion	Possible when severe	Possible when severe
Fruity-smelling breath	Possible with DKA	No
Seizure or unconsciousness	Possible in severe crisis	Possible with severe hypoglycemia

Because several symptoms overlap, checking your glucose is more reliable than trying to determine whether your blood sugar is high or low based only on how you feel.

Symptoms of High Blood Sugar (Hyperglycemia)

Hyperglycemia means there is too much glucose in your bloodstream. High blood sugar can develop when your body does not have enough insulin, cannot use insulin effectively, or when food, illness, stress, inactivity or certain medications cause glucose to rise.

High blood sugar symptoms often develop gradually and may include:

• Increased thirst
• Frequent urination
• Fatigue or weakness
• Blurred vision
• Headache
• Difficulty concentrating
• Slow-healing wounds
• Frequent infections

Some people have few noticeable symptoms even when glucose is elevated. Mayo Clinic notes that symptoms of hyperglycemia may not become noticeable until glucose is above approximately 180–200 mg/dL, although this varies by person.²

If you frequently have high readings, discuss the pattern with your healthcare provider rather than relying on symptoms alone.

Symptoms of Low Blood Sugar (Hypoglycemia)

Hypoglycemia occurs when blood glucose falls too low. It is especially important for people who use insulin or other diabetes medications that can cause hypoglycemia.

Common low blood sugar symptoms include:

• Shakiness
• Sweating
• Hunger
• Dizziness or light-headedness
• Irritability or nervousness
• Weakness
• Rapid heartbeat
• Difficulty concentrating
• Confusion

The American Diabetes Association (ADA) defines Level 1 hypoglycemia as glucose below 70 mg/dL but at least 54 mg/dL, and Level 2 hypoglycemia as glucose below 54 mg/dL. Severe, or Level 3, hypoglycemia is an event requiring help from another person, regardless of the glucose reading.¹

Some people develop impaired hypoglycemia awareness, meaning they may not experience typical warning signs such as shaking, sweating or hunger when their glucose becomes low.¹

How to Tell if Your Blood Sugar Is High or Low

Certain symptoms can provide clues:

• Thirst and frequent urination are more characteristic of high blood sugar.
• Shaking, sweating and sudden hunger are more characteristic of low blood sugar.
• Fatigue, weakness, headache, blurred vision and difficulty concentrating can occur with changing glucose levels.
• Confusion can occur when either high or low blood sugar becomes severe.

If possible, check your glucose with a meter or CGM when symptoms occur rather than guessing based on how you feel.

For help interpreting your readings throughout the day, see DiabetesKnow’s blood sugar charts.

Understanding Your Glucose Levels

For low blood sugar, the ADA uses these classifications:¹

Blood Sugar Level	Classification
Below 70 to 54 mg/dL	Level 1 hypoglycemia
Below 54 mg/dL	Level 2 hypoglycemia
Severe event requiring assistance	Level 3 hypoglycemia

High blood sugar is less straightforward because glucose targets depend on when you last ate, whether you have diabetes and your individual treatment plan.

For diagnosis, a fasting plasma glucose of 126 mg/dL or higher or a two-hour glucose of 200 mg/dL or higher during an oral glucose tolerance test meets ADA criteria for diabetes. A random plasma glucose of 200 mg/dL or higher can also meet diagnostic criteria when classic symptoms of hyperglycemia or a hyperglycemic crisis are present. In the absence of unequivocal hyperglycemia, confirmatory testing is generally required.³

For a more detailed explanation, see normal blood sugar levels.

What to Do When Your Glucose Is Out of Range

If Your Blood Sugar Is Low

For most conscious people who can safely swallow, the ADA recommends treating glucose below 70 mg/dL with fast-acting glucose or another carbohydrate containing glucose and checking again after 15 minutes. Fifteen grams of carbohydrate is commonly used, although individual treatment needs can vary.¹

Examples include glucose tablets, glucose gel, fruit juice or regular non-diet soda.

If someone has severe hypoglycemia and cannot safely consume carbohydrates, glucagon may be needed. Seek emergency medical help if the person is unconscious, having a seizure or unable to swallow safely.

If Your Blood Sugar Is High

Follow the treatment plan provided by your healthcare team. Depending on your individual plan, this may include checking your glucose again, staying hydrated, taking prescribed medication or a correction dose of insulin, and checking ketones when appropriate.

Do not take extra insulin or change medication doses unless this is part of your prescribed diabetes management plan.

When to Seek Emergency Medical Help

Severe low blood sugar can cause confusion, seizures, loss of consciousness or coma. Level 3 hypoglycemia requires assistance from another person and should be treated immediately.¹

Very high blood sugar can also lead to serious emergencies such as diabetic ketoacidosis (DKA) or hyperglycemic hyperosmolar state (HHS).

Warning signs of a hyperglycemic emergency can include:

• Nausea or vomiting
• Abdominal pain
• Severe dehydration
• Rapid or deep breathing
• Fruity-smelling breath
• Confusion
• Loss of consciousness

DKA and HHS are potentially life-threatening and require prompt medical treatment.¹

FAQs

References

1. ADA — Glycemic Goals, Hypoglycemia, and Hyperglycemic Crises: Standards of Care in Diabetes—2026 ADA 2026 Standards — Section 6 [↩] [↩] [↩] [↩] [↩] [↩] [↩] [↩] [↩] [↩]
2. Mayo Clinic — Hyperglycemia in Diabetes: Symptoms and Causes Mayo Clinic — Hyperglycemia in Diabetes [↩] [↩]
3. ADA — Diagnosis and Classification of Diabetes: Standards of Care in Diabetes—2026 ADA 2026 Standards — Section 2 [↩]