Are you feeling more fatigued than usual? Do you have unexplained aches and pains? Struggling to do mileage that usually comes easy to you? Chances are, you are dehydrated and you don't know it. Distance running in India means running in the heat and humidity for most of the year. With extreme heat conditions becoming more frequent, heatwaves getting longer, it has become critical to understand the principles of hydration. What does dehydration do to you? What can you do to prevent it? Does only water help, or do you need electrolytes? Ultramarathon runner Dr Chauhan, who organises one of India's toughest marathons, La Ultra in Ladakh, tackles the tricky subject.