This 25-year-old marketing executive mostly spends his day criss-crossing the city on his motorcycle, moving from one client meeting to another, braving the furnace-like midday heat. Like many young professionals, he believed he was doing the right thing by drinking water constantly. He stopped frequently to refill his bottle, consuming nearly five litres through the day. What he did not do was eat. A rushed morning meant he skipped breakfast and his lunch break was lost in back-to-back meetings. He consumed no fruit, no electrolyte drink, no oral rehydration solution — only plain water. That proved costly.By evening, he began to feel strangely light-headed. Nausea followed. He dismissed it as exhaustion. He pushed on, determined to finish his final appointments. Within hours, his speech became sluggish. He grew unusually drowsy and disoriented. Alarmed colleagues rushed him to our emergency department. Blood investigations revealed that his sodium level had plummeted to 124 mEq/L, far below the normal range of 135 to 145 mEq/L. The diagnosis was acute hyponatremia — a dangerous fall in blood sodium caused by excessive salt loss through sweating, worsened by overconsumption of plain water.His case is far from isolated. Across India, where summer temperatures are now routinely touching 44 to 47 degrees Celsius, hospitals are seeing a rise in heat-related electrolyte disturbances that often masquerade initially as simple fatigue.When heat sucks up vital body saltsSweating is the body’s primary cooling mechanism. As sweat evaporates from the skin, it dissipates heat and helps regulate body temperature. Yet sweat is not merely water. It carries with it sodium, chloride, potassium and other essential electrolytes — charged minerals that regulate nerve impulses, muscle contractions, fluid balance and heart rhythm.Under normal conditions, these losses are modest and easily replenished through regular food and drink. But under prolonged exposure to extreme heat, particularly when coupled with physical exertion, the losses can become significant.The problem deepens when hydration is approached incorrectly. In India, the common advice during summer is to “drink a lot of water.” While well-intentioned, this message is incomplete. Water alone cannot replace the electrolytes being lost. In fact, when consumed excessively without adequate salt intake, it can dilute sodium levels in the bloodstream, creating precisely the kind of dangerous imbalance seen in the young executive’s case. You need electrolyte-infused water.The hidden danger of low sodiumSodium is crucial because it regulates the movement of water into and out of cells, particularly in the brain. When sodium levels drop too low, water shifts into cells, causing them to swell. In the brain, where the skull leaves no room for expansion, this swelling can rapidly become life-threatening. The earliest symptoms are often deceptively mild — headache, fatigue, dizziness, nausea and confusion. These are easily mistaken for heat exhaustion or simple overwork.Story continues below this adAs sodium levels continue to fall, symptoms can escalate dramatically. Drowsiness deepens into altered consciousness. Seizures may occur. In severe cases, patients can slip into coma.What makes hyponatremia especially dangerous during Indian summers is that it often affects young, otherwise healthy individuals who underestimate the seriousness of their symptoms. Outdoor workers, delivery personnel, field executives, traffic police officers and construction workers are particularly vulnerable.The other extreme: HypernatremiaHypernatremia develops when water loss exceeds replacement. This typically occurs when someone exposed to intense heat sweats profusely but fails to drink enough fluids. As body water content drops, sodium becomes increasingly concentrated in the blood.Unlike hyponatremia, which causes cells to swell, hypernatremia causes cells to shrink as water is drawn out of them. The brain is again particularly sensitive to this shift. The symptoms often begin with intense thirst and dryness of the mouth, but can progress to irritability, restlessness, muscle twitching, confusion and seizures. In severe cases, hypernatremia can cause permanent neurological damage.Story continues below this adThus, summer heat presents a paradoxical challenge: drinking too little water can be dangerous, but drinking large amounts of plain water without electrolyte replacement can be equally hazardous.Potassium: The often-overlooked casualtyWhile sodium tends to dominate discussions around heat-related illness, potassium deserves equal attention. Potassium is indispensable for muscle function and electrical conduction within the heart. Even minor disturbances can have profound consequences.Heavy sweating, coupled with skipped meals and poor nutritional intake, can lead to hypokalaemia — low blood potassium. This often manifests as muscle weakness, painful cramps, profound fatigue and, in serious cases, disturbances in heart rhythm. The danger is amplified in those who are already nutritionally depleted or those experiencing vomiting due to heat illness.Conversely, severe dehydration can compromise kidney function, impairing the body’s ability to excrete potassium. This may result in hyperkalaemia, a potentially lethal condition that can trigger sudden cardiac arrest. The balance is extraordinarily delicate.Story continues below this adPrevention requires smarter hydrationThe lesson from the young executive’s ordeal is simple but vital: hydration is not just about water.The body requires replacement of both fluid and dissolved salts. Oral rehydration solutions, buttermilk with a pinch of salt, coconut water, lemon water with salt and sugar, and electrolyte-rich foods can help restore what sweating takes away. Equally important is regular food intake.Timing also matters. Outdoor exertion during the fiercest afternoon hours should be minimised wherever possible. Frequent shaded breaks and early recognition of warning symptoms can prevent progression to medical emergency.The image of heatstroke as a dramatic collapse under the blazing sun is outdated. Increasingly, the danger lies in quieter, less visible disturbances unfolding at the cellular level — electrolyte shifts that begin with mild dizziness and end, if ignored, in neurological crisis. The 25-year-old executive recovered because he reached medical care in time. Many may not, so sip electrolyte-infused water every half hour.(Dr Tickoo is Director, Internal Medicine, Max Healthcare)