What hyponatremia is, and the symptoms of low sodium

What Is Hyponatremia?
Hyponatremia occurs when the concentration of sodium in your blood falls below normal levels (less than 135 mEq/L). Sodium is essential for maintaining fluid balance, nerve impulses and muscle function. When sodium levels drop too low, water moves into cells and causes them to swell. In the brain, this swelling can lead to significant symptoms and, in severe cases, life-threatening complications.

How Common Is It?
Hyponatremia affects people of all ages but is especially common in:

• Older adults taking certain medications
• People with chronic illnesses (heart failure, kidney disease, liver disease)
• Endurance athletes who drink excessive water without replacing electrolytes

Understanding the causes and recognizing hyponatremia symptoms early can help you get proper treatment and avoid serious problems.

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Causes of Low Sodium

Hyponatremia can develop through several mechanisms. Common causes include:

• Excessive water intake
• Certain medications (diuretics, antidepressants, anticonvulsants)
• Syndrome of inappropriate antidiuretic hormone secretion (SIADH)
• Heart failure, liver cirrhosis, kidney disease
• Adrenal insufficiency (Addison’s disease)
• Severe diarrhea or vomiting
• Hormonal changes

Each of these conditions either dilutes sodium in the body or causes sodium loss.

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How Hyponatremia Develops

When sodium levels drop, water shifts from the blood into cells to balance concentrations. In most tissues this causes discomfort but little immediate danger. In the brain, however, swollen cells have no room to expand. This leads to increased pressure within the skull and triggers the hallmark signs of hyponatremia.

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Recognizing Hyponatremia Symptoms

Symptoms vary by how quickly sodium falls and how low levels go. Here’s what to watch for:

Mild to Moderate Hyponatremia (Serum Na 125–135 mEq/L)

• Headache
• Nausea or vomiting
• Fatigue, lethargy
• Muscle weakness or cramps
• Restlessness or irritability
• Difficulty concentrating

Severe Hyponatremia (Serum Na <125 mEq/L)

• Confusion, disorientation
• Slurred speech
• Coordination problems, unsteady gait
• Hallucinations or delirium
• Seizures
• Loss of consciousness
• Respiratory arrest (rare but critical)

Symptoms that develop over hours (acute hyponatremia) tend to be more severe than those appearing over days or weeks (chronic hyponatremia). Always treat new or worsening neurological signs as an emergency.

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Diagnosing Low Sodium

A healthcare provider will typically order:

1. Serum sodium concentration
2. Plasma osmolality (to confirm true hyponatremia)
3. Urine osmolality and sodium (to determine cause)
4. Blood tests for kidney, liver and adrenal function

These tests help pinpoint whether the problem is due to excess water retention, sodium loss or hormone imbalance.

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Treatment Approaches

Management depends on severity and underlying cause:

• Mild, asymptomatic cases
– Fluid restriction
– Adjust or stop offending medications
– Monitor sodium levels closely

• Moderate to severe cases
– Hospital admission
– Intravenous (IV) fluids: isotonic or hypertonic saline
– Medications to block antidiuretic hormone (in SIADH)
– Treat underlying conditions (heart failure, adrenal insufficiency)
– Careful correction rate (no more than 6–8 mEq/L per 24 hours) to avoid brain damage

Your medical team will tailor treatment and monitor sodium levels and neurologic status every few hours in severe cases.

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Preventing Dangerous Swings

To lower risk:

• Follow fluid-restriction guidelines if advised.
• Don’t overhydrate during endurance events—use sports drinks with electrolytes.
• Review your medications with a doctor or pharmacist.
• Manage chronic health conditions (heart, liver, kidney) with regular check-ups.

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When to Seek Medical Attention

Contact your healthcare provider or go to the emergency department if you experience:

• Sudden confusion or difficulty speaking
• Seizures or fainting
• Severe headache not relieved by over-the-counter painkillers
• Persistent nausea, vomiting or abdominal pain
• Rapid onset of weakness or difficulty walking

For milder concerns—especially if you notice gradual changes—you might also consider doing a free, online symptom check, using the doctor approved Ubie Symptom Checker to help guide your next steps.

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Key Takeaways

• Hyponatremia is low blood sodium (<135 mEq/L) that can range from mild to life-threatening.
• Early signs include headache, nausea and fatigue; serious signs include confusion, seizures and coma.
• Diagnosis requires blood and urine tests.
• Treatment focuses on safely restoring sodium levels and addressing the underlying cause.
• Speak to a doctor about any alarming or persistent symptoms—prompt care can prevent serious complications.

If you suspect you have hyponatremia or notice any concerning symptoms, don’t wait. Speak to a doctor about evaluation and treatment right away.