Yeah, when I did a bike tour through the south in late july early august I lost too much salt. It was a terrible feeling cause we made camp and I couldn't stop from being queezy until I ate some ramen noodles (lots of salt). I cook a lot so when I can tell I'm low on salt I've got potassium salt (called "no salt") and sodium salt that I can throw in.
Oh, and with hydrating myself I went from going 13mph average over and 1:45 to going 16.1mph average over 2 hours. The trick to staying hydrated really is just drinking a lot off the bike.