[gpm]

If you're about to die of dehydration - and have been rehydrating with fresh water - you'll be low on salt too so a bit of seawater should in principle be in the right direction for both and help. In practice I wonder if your digestive tract might object to the salt water too strongly for this to work though.

If you're about to die of dehydration - from sweating - and have not been rehydrating you're already also hypernatremic (too salty) as well so I sort of doubt it would help. Sweat is less salty than your blood so it increases salt concentration.

[throwaway173738]

It depends. Hypernatremia refers specifically to sodium but doesn’t speak to potassium or calcium. You need all three in proper balance for your body. So you can sweat a bunch and still need to take in more salts because the balance is off.