How do I know when my sodium is low?

December 24, 2025 •

3 min read

According to Mayo Clinic, hyponatremia, or low blood sodium, is the most common electrolyte disorder found in hospitalized patients. Recognizing the signs and symptoms is crucial for early detection, as symptoms can range from mild and subtle to severe and life-threatening.

Quick Summary

This article outlines the signs and symptoms associated with low sodium, from mild indicators like fatigue and headache to severe issues such as seizures and confusion. It details common causes, identifies risk factors, and provides guidance on when to seek medical attention for hyponatremia.

Key Points

Fatigue and Nausea: Common early warning signs of low sodium include unexplained tiredness, headache, and a feeling of nausea or vomiting.
Muscle Cramps and Spasms: Low sodium levels can cause muscle weakness, cramps, or spasms due to its effect on muscle function.
Mental Changes: Look for signs of confusion, restlessness, or irritability, which indicate that low sodium is affecting the brain.
Acute vs. Chronic: Symptoms can be less severe if sodium drops gradually (chronic), but more pronounced and sudden if it drops quickly (acute).
Severe Symptoms Require Emergency Care: Seizures, loss of consciousness, and severe vomiting warrant immediate medical attention.
Diagnosis Requires a Blood Test: A medical professional is needed to confirm hyponatremia, as symptoms alone are not enough for a definitive diagnosis.

Sodium is an essential electrolyte that plays a vital role in maintaining the balance of water in and around your cells, as well as helping with nerve function and muscle contraction. When the concentration of sodium in your blood drops below the normal range (135 to 145 mEq/L), it results in a condition called hyponatremia.

Early and Moderate Signs of Low Sodium

Early symptoms of hyponatremia can often be non-specific and are easily mistaken for other conditions. These symptoms often appear gradually, especially in cases of chronic hyponatremia where levels drop slowly over time.

Common signs to look for:

Fatigue and low energy: A persistent feeling of tiredness or lethargy that doesn't improve with rest can be an early red flag.
Headache: Swelling of the brain cells due to the water imbalance can cause headaches.
Nausea and vomiting: These digestive issues are a common symptom of low sodium.
Muscle weakness, spasms, or cramps: Low sodium affects muscle function, leading to these muscular issues.
Restlessness and irritability: Changes in mood or an agitated state can be linked to hyponatremia.
Loss of appetite: A general disinterest in eating or a loss of hunger is another potential sign.

Severe and Critical Symptoms

If sodium levels drop quickly (acute hyponatremia) or fall to severely low levels (typically below 120 mEq/L), the symptoms can become much more serious and require immediate medical attention.

Life-threatening indicators include:

Confusion and disorientation: Significant changes in mental state, an inability to think clearly, or extreme confusion can occur.
Seizures: Severe hyponatremia can disrupt the electrical charges of nerve cells, potentially causing convulsions.
Loss of consciousness or coma: In the most critical cases, the condition can progress to a loss of consciousness.
Severe vomiting: Persistent and intense vomiting can be a sign that the condition is worsening.
Brain swelling (cerebral edema): When brain cells swell due due to fluid shifts, it can lead to permanent damage or be fatal.

Common Causes of Low Sodium

Several factors can lead to low sodium levels. Identifying the cause is crucial for effective treatment. Common culprits include:

Drinking too much water: Especially common in endurance athletes who consume excessive plain water during events like marathons, which dilutes blood sodium.
Certain medications: Diuretics (water pills), some antidepressants, and pain medicines can alter sodium levels.
Underlying health conditions: Heart failure, kidney disease, and liver disease can cause fluid buildup that dilutes sodium.
Severe vomiting or diarrhea: Prolonged or severe instances can cause significant fluid and electrolyte loss.
Hormonal changes: Conditions like Addison's disease or low thyroid hormone levels can disrupt the body's sodium and water balance.
Recreational drugs: The recreational drug ecstasy has been linked to severe and even fatal cases of hyponatremia.

Low Sodium vs. Normal Sodium Symptoms

To help understand the difference, consider this comparison of typical symptoms and general state associated with each:


Characteristic	Low Sodium (Hyponatremia)	Normal Sodium Balance
Energy Levels	Significant fatigue, lethargy, low energy.	Steady energy levels throughout the day.
Mental State	Confusion, disorientation, restlessness, irritability.	Clear thinking, stable mood.
Muscular Health	Weakness, spasms, or cramps.	No unusual weakness, cramps, or spasms.
Digestive Issues	Nausea, vomiting, loss of appetite.	Healthy appetite and normal digestion.
Headaches	Persistent or worsening headaches.	Infrequent headaches.
Neurological Impact (Severe)	Seizures, coma, loss of consciousness.	No neurological issues.

What to Do If You Suspect Low Sodium

If you experience any mild or moderate symptoms and have risk factors, it is important to consult a healthcare professional. They can perform a blood test, which is the only way to definitively diagnose low sodium. If you or someone you know exhibits severe symptoms like confusion, seizures, or loss of consciousness, seek emergency medical care immediately.

Treatment depends on the severity and underlying cause. It can range from simple fluid restriction and adjusting medication for mild cases to more intensive intravenous sodium treatment for severe hyponatremia.

Conclusion

Knowing the signs of low sodium is the first step toward safeguarding your health. While mild symptoms like fatigue and headaches can often be overlooked, recognizing them early can prevent the condition from escalating. Pay attention to how your body feels, especially if you engage in intense exercise, take certain medications, or have a chronic illness. By understanding the risk factors and heeding the body's warning signals, you can take prompt action and seek the necessary medical care to restore proper electrolyte balance and prevent serious complications.

For more detailed information on sodium's role in the body, visit the National Institutes of Health (NIH) website.

Frequently Asked Questions

The medical term for low sodium in the blood is hyponatremia. A person is diagnosed with hyponatremia when their blood sodium level drops below 135 milliequivalents per liter (mEq/L).

Mild hyponatremia may cause subtle or no symptoms, especially if it develops slowly. Common signs can include headache, fatigue, mild nausea, muscle cramps, and general restlessness.

You should call your healthcare provider if you have risk factors for hyponatremia and experience symptoms like persistent nausea, headaches, fatigue, or muscle cramps. Seek emergency care immediately for severe symptoms like confusion, seizures, or loss of consciousness.

Yes, drinking an excessive amount of water can cause low sodium. This is a common cause among endurance athletes who lose sodium through sweat and then overhydrate with plain water, diluting their blood sodium levels.

Yes, older adults are at a higher risk for hyponatremia due to a greater likelihood of having chronic diseases, taking certain medications, and age-related physiological changes that affect sodium balance.

When sodium levels are low, water moves into the body's cells, causing them to swell. Brain cells are particularly sensitive to this swelling (cerebral edema), which leads to many of the severe neurological symptoms, including confusion, seizures, and coma.

Low sodium is diagnosed through a blood test that measures the concentration of sodium in your blood. Your doctor may also order urine tests to help determine the underlying cause.