Low blood sodium (hyponatremia) may lead to rapid and dangerous swelling of the brain. It's a common condition in older adults and in people with certain chronic conditions. Causes include:

• Liver disease
• Kidney (renal) failure
• Heart failure
• Thyroid or adrenal gland disease
• Medications, such as certain diuretics, antidepressants and pain medications
• Excessive thirst (polydipsia) and water drinking, but this is uncommon

Signs and symptoms of low blood sodium include:

• Confusion
• Fatigue
• Decreased levels of consciousness

Because these signs and symptoms are nonspecific and occur in many conditions, the only way a doctor can confirm low blood sodium is by a blood test.

Treatment is directed at the underlying cause, if it can be identified and corrected. Your doctor may advise you to temporarily cut back on fluids to increase blood sodium levels.