If by “abnormal sugar levels” you mean blood glucose that is either too high or too low, the body can send several warning signals. The important point is that some people—especially those with prediabetes or type 2 diabetes—may have few or no obvious symptoms, so symptoms alone cannot reliably tell you whether blood sugar is abnormal.
Signs of high blood sugar (hyperglycemia)
When blood glucose remains elevated, common warning signs include:
- Excessive thirst — you may feel unusually thirsty even after drinking.
- Frequent urination — especially getting up repeatedly at night.
- Increased hunger — feeling hungry despite having recently eaten.
- Unusual tiredness or weakness — high glucose can leave you feeling drained.
- Blurred vision — changes in glucose can temporarily affect the eye’s ability to focus.
- Unexplained weight loss — more commonly seen when diabetes is significantly uncontrolled.
- Slow-healing cuts or sores.
- Repeated infections, including urinary, skin, or yeast infections.
A person may dismiss these symptoms as simply being tired, drinking too much water, aging, or being stressed. That can allow high blood sugar to continue unnoticed.
Signs of low blood sugar (hypoglycemia)
Low blood sugar can develop much more suddenly. For many people with diabetes, below 70 mg/dL is considered low. Symptoms may include:
- Shaking or trembling
- Sweating or feeling clammy
- Sudden hunger
- Fast or irregular heartbeat
- Dizziness or lightheadedness
- Headache
- Irritability or anxiety
- Weakness or fatigue
- Difficulty concentrating
- Confusion
- Blurred vision or difficulty speaking
If glucose falls severely, a person can lose consciousness or have a seizure, making severe hypoglycemia an emergency.
Why some people don’t recognize the warning signs
This is particularly important. Someone who experiences repeated episodes of low blood sugar can develop hypoglycemia unawareness. Their usual warning symptoms may become weaker or disappear, meaning glucose can fall to a dangerously low level before they realize something is wrong.
High blood sugar can also be deceptive because it may develop gradually and cause subtle symptoms—or no symptoms at all. NIDDK notes that many people with diabetes don’t know they have it because they have no obvious symptoms.
When symptoms require urgent attention
Very high blood sugar accompanied by extreme tiredness, difficulty breathing, fruity-smelling breath, confusion, fainting, or significant illness can indicate diabetic ketoacidosis (DKA), which requires immediate medical attention.
The safest approach is not to rely on how you feel alone. If you have symptoms or risk factors, blood glucose testing and appropriate diabetes testing such as an A1C can determine whether your glucose is actually abnormal.
If you want, I can also give you a detailed list of the 20 early warning signs of high blood sugar that people commonly ignore, including what each symptom means and when it becomes concerning.