Is the sense for salt depending on the electrolyte level in our body?
Is this possible or am I just hallucinating?


Certainly possible, but I'd peg the mechanism closer to Sensitization or De-sensitization of the neurons involved so that when you finally ingest some salt the sensation is different. The sodium and chloride levels of the ingested material wouldn't have a direct effect on the level of De-/Sensitization, but rather how low your stores are or how long you've gone without.


  So, I imagine it like this....


What you broadly described is how regular sodium receptors work. They will work that way regardless of what you've been doing, and doesn't really explain an increase or decrease in your ability to taste salt - the signals will fire either way. 

Check out the action of the Capsaicin receptor and how it changes sensitivity over short periods of time. I'm betting the phenomenon you're describing will be closer to this (an increase or decrease in the number of sodium receptors in response to the abundance of salts or lack-thereof) than an immediate mechanism from the drink itself.