Per the article, some people got into trouble, because they were sweating
excessivley (usually atheletes) and just like you, "they were losing larges
amounts of both water and sodium in their sweat but they were replacing
their fluid loses with water only." You need to replace that sodium, or
your problem will continue. If you're sweating a ton, you have to replace
the salt, not just the water.
If you don't like sport drinks or salt tablets, try eating some salty foods
such as potato chips or salted nuts. We do our boating on Lake Mojave.
Temps avg 105 to 115 degF. I've seen the consequence of all water and no
salt. The symptons are similar to dehydration.