Hot weather also raises your heartrate by about 10 bpm, which means you're more likely to hit your max heartrate. That's when you puke - the vasovagal response from staying at a very high heartrate.

As for the extra-salty sweat, this is part of acclimation. Once you're acclimated to the warmer season your sweat will be more diluted.

Drink fluids, remember to take electrolytes, and just take it easy until you are more used to the heat. It never does get comfortable, but it will get a little better.