‘You are sweating half a litre an hour’: what happens to your body when dehydrated – and how to avoid it

‘How much you should drink to prevent dehydration depends on things like your weight, age, general health, level of activity, and variables such as wind, shade and humidity.’ Photograph: skaman306/Getty Images

On day two of the Three Capes walk in Tasmania, which I was looking forward to as the easiest due to being flat, I found myself walking in blazing sun across an expanse of scrub with no shade. Despite drinking regularly from the two litres I was carrying, I started to feel weak, disoriented and desperate.

Eventually I could go no further. It was an unseasonably warm day. I was sweating moderately but not excessively. I became slightly light-headed, and a kind of apathy and despair settled on me, almost like I had lost the will to live. In my tendency for melodrama, I sobbed “just leave me here” to my alarmed husband.