I actually supplement my sodium intake daily - I consume 2 bouillon cubes before working out each afternoon. I don’t eat more than 20g to 25g of carbs each day and my kidneys excrete sodium immediately. Absent my lunch of 2 bouillon cubes each day, I can’t make it through a workout without a massive headache and low performance.
But, I do agree that most Americans consume far too much sodium. People who eat ANY processed food whatsoever get too much.
Those are two of the most common symptoms of heat exhaustion. Others are vertigo, fainting, and severe muscle cramps.
Long ago, I learned from a nutritionist that what lies behind those symptoms, is the loss of essential minerals during heavy exertion/perspiration, most especially salt. The way to prevent it, is to simply supplement with natural salt (sea salt tabs work best).
In fact, lots of older guys will tell you that they were issued salt tablets in their military training days. I work outdoors in the construction trades and carry a bottle of sea salt tablets with me at all times. On days when I forget to take them, I get some of the symptoms you mentioned. On days I don't forget, I never experience any of them.