Final answer:
Euvolemic hyponatremia occurs due to an imbalance of sodium or dilution of sodium from water retention. It leads to increased entry of water into cells, causing swelling that can lead to brain damage or death.
Step-by-step explanation:
Euvolemic hyponatremia can occur due to an imbalance of sodium in the body's other fluid compartments or from dilution of sodium due to water retention related to edema or congestive heart failure. At the cellular level, hyponatremia leads to increased entry of water into cells by osmosis, resulting in swelling of cells including red blood cells and neurons in the brain. This swelling can cause brain damage or even death.